really slow PLL...

[Don]

Don Y wrote:

Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:
bitrex wrote:

snip

Yeah I don\'t quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really

How is \"really well\" defined? In the domain of human auditory perception?

In this case, isn\'t \"really well\" defined as an absence of sour note(s)?

That assumes the synthesis uses the same clock as timing. I think the
discussion here has been wrt durations/intervals.

How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents (\"perfect pitch\")?

Can\'t everyone\'s ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?

Perfect pitch is more than just \"naming a note\".

It\'s all but impossible for me personally to ignore the sourness of
cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.

How \"sour\" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the \"previous note\" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)

https://neurosciencenews.com/pitch-detection-music-21087/

This is a reference note (middle C) followed by the same note \"soured\"
by 12 cents:

https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav
Here\'s *one* cent difference:

https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav

And 24 cents (about the point of \"normal\" perception):

https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav

If your device\'s *timing* was off by 0.05%, would that be consequential?

Very interesting information. Thank you.
It\'s easy for me to hear the one cent difference, how about you? My
audio perception comes in handy when it\'s time to tune a keyboard. Some-
times musicians purposefully vary tones by a few cents in order to
produce vibrato.

Could you hear a middle C \"soured\" by one cent when it follows a
(correct) C-sharp immediately preceding it? Or, vice versa?

*I* can\'t. My threshold is closer to 10 cents and rely on electronic
devices when tuning instruments.

And, if every note was \"off key\" by 10 cents, I\'d not recognize the
tony.

In regards to your 0.05% device timing question, the answer is: it
depends. A 0.05% device timing variance in my Power Bank Keepalive:

https://crcomp.net/mp3mod/index.php

for instance, is inconsequential.

In the context of this thread, it likely has an impact. A cent is
about 500PPM (though in the frequency domain)

Your question about a one cent following note difference perception is
interesting. And, it needs to be followed up by me, so to speak.
For some unknown reason, the only thing to truly satisfy me is to
tune instruments by ear.

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

On Fri, 22 Jul 2022 06:20:58 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de
wrote:

Am 21.07.22 um 01:20 schrieb John Larkin:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.


I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz.
The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won\'t be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.

Where does the 10 MHz come from?

https://en.wikipedia.org/wiki/GPS_disciplined_oscillator

\"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop.\"

That\'s what I meant: the 10M xo is locked to the 1 PPS GPS output.

The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.

GPS timing isn\'t completely perfect in reality. Antennas blow off roofs,
contractors cut cables etc. Even losing sync for a minute is sort of a big
deal. As you mentioned, jitter is the real problem. There are tradeoffs to
making a flywheel thats too heavy so to speak.

For really fussy stuff, one might have multiple GPS receivers and a quorum
of local 10Mhz oscillators. In fact, 10Mhz is a dinosaur relic for modern
stuff too. We\'ve got racks of 10Mhz oscillators and equipment to monitor
any phase shift between local oscillators and GPS sources. It\'s all going
to the dumpster when somebody finally notices it\'s been powered down and
forgotten about.

Fairly accurate nS resolution timing is possible in computers these days,
with the right tricks.

I triggered a scope from a very good ovenized XO and looked at the
rising edge of a rubidium. The edge looked solid, as if it was
internal triggered. Checking every 20 minutes or so, it ws slowly
creeping across the screen, at 5 ns/cm.

I believe they somehow pair the rubidium clocks with another quartz
crystal, even in those new tiny physics modules. I\'ve not had a chance to
tear apart a rubidium clock yet, or the ovenized stuff. They come in
little metal boxes, that remind me of TV tuners.

I\'ll be doing something similar, locking my 40 MHz clock to some 1 PPS
input, the difference being that I don\'t mind a few us of jitter, so I
can lock quick and crude.

Do you have to worry about fun issues like an the timestamp of a signal
being received before it was even transmitted between pieces of equipment?

It a multi-channel power supply!

You were also asking about timestamping in other posts. Not entirely sure
what you\'re upto in the end, but it might be interesting.

 

[Jan Panteltje]

On a sunny day (Fri, 22 Jul 2022 09:01:52 -0700) it happened
jlarkin@highlandsniptechnology.com wrote in
<vnhldhh5vjech8rgksjrmss5djbgfndtqj@4ax.com>:

On Thu, 21 Jul 2022 18:04:22 -0700, Don Y
blockedofcourse@foo.invalid> wrote:

On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. Do
you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really

How is \"really well\" defined? In the domain of human auditory perception?

Sound travels about a foot per millisecond, so we are used to multiple
time delays. A marching band sounds coordinated to us.

I am thinking about vision a lot lately too. Each eye acquires a
differently scaled image that changes constantly. There are
millisecond-level changes in focus and parallax. I can put my glasses
on, or not, and magnification surely changes. Somehow a brain acquires
two images and distorts them in real time so that all the bits align.

One has much better resolution using two eyes than either alone can
provide.

Nice trick. Sound must work like that to, extensive post-processing of
acquired inputs. Probably time shifting parts of the spectrum, or
something more complex, multiple cross-correlations.

Yes vision is a very interesting thing, been working on that for most of my life (TV etc)
As I am not from this planet as you likely guessed I can see things from sound only
But today it got even weeder...
I had the TV on, switched it off, sat on the bench relaxing with eyes closed
all of the sudden I visualized a field of purple I think it was flowers...
Very bright and strong..
switched on the TV and there is was : same field.
Still puzzled, only thing on was the sat receiver (connected via HDMI to the TV)
but TV was off.
I have tried some processing sound to vision but I think we need a neural net
copy from the brain\'s visual part.
RF to vision?
Work on the 4G tower here ended at 6 PM today, at about 5 my 4G signal was back at 100%
was depending on signal from a far away tower for the last 3 or 4 days,,, dropped when it rained..
but.. being impatient .. had checked on the ad dropped in my mailbox for fiber connection..
checked out their site, not bad and just as expensive but much faster than 4 G and no data limit..
but may take month before they are at my house installing stuff.,.
fiber as backup not a bad idea... not very portable though.

As to depend on GPS or GLONASS or what have you these days for professional test equipment
seems a no-no to me, often there is no coverage,

And as to connections, BNC sucks.
Ethernet cable connectors suck too but you can do a whole lot with those connections
and protocols and you can get good time signals from the net.
I have a Casio radio watch accurate to the second.. sure you can jam that 77.5 kHz too
but so far it has always worked here, what do you US guys use? WWVB?
Automatic summer-winter time switch too

 

[Cydrome Leader]

jlarkin@highlandsniptechnology.com wrote:

On Fri, 22 Jul 2022 10:37:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de
wrote:

Am 22.07.22 um 04:47 schrieb jlarkin@highlandsniptechnology.com:

Where does the 10 MHz come from?

https://en.wikipedia.org/wiki/GPS_disciplined_oscillator

\"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop.\"

That\'s what I meant: the 10M xo is locked to the 1 PPS GPS output.

No. The 1pps is asserted when the CPU thinks it\'s closest to
the \"right\" clockcycle. It could be off by half a cycle.
There is no need for 10 MHz, one could have chosen a nice
multiple of the desired baud rate.


Our GPS receivers output 1 PPS and 10 MHz. Argue with Wikipedia.

What he\'s trying to say is it may not be perfect 10 million cycles between
every 1PPS pulse. For most stuff, this is good enough. For the metrology
folks, using strong words like exactly or in this case \"locked\" will
always cause an argument.

 

[John Walliker]

On Friday, 22 July 2022 at 17:02:04 UTC+1, jla...@highlandsniptechnology.com wrote:

On Thu, 21 Jul 2022 18:04:22 -0700, Don Y
blocked...@foo.invalid> wrote:

On 7/21/2022 7:04 AM, bitrex wrote:
You really need to define longterm before the problem becomes well posed. Do
you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each play one
voice of the Maple Leaf Rag via MIDI and they all stay synced together really

How is \"really well\" defined? In the domain of human auditory perception?
Sound travels about a foot per millisecond, so we are used to multiple
time delays. A marching band sounds coordinated to us.

I am thinking about vision a lot lately too. Each eye acquires a
differently scaled image that changes constantly. There are
millisecond-level changes in focus and parallax. I can put my glasses
on, or not, and magnification surely changes. Somehow a brain acquires
two images and distorts them in real time so that all the bits align.

One has much better resolution using two eyes than either alone can
provide.

Nice trick. Sound must work like that to, extensive post-processing of
acquired inputs. Probably time shifting parts of the spectrum, or
something more complex, multiple cross-correlations.

There is cross-correlation between left and right ears in the brainstem which
is involved in determining the direction of sound sources. Detectable time
differences are remarkably small. (I would have to look it up to give a number.)
John

 

[Lasse Langwadt Christensen]

fredag den 22. juli 2022 kl. 16.46.36 UTC+2 skrev Don Y:

On 7/22/2022 7:17 AM, Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:
bitrex wrote:

snip

Yeah I don\'t quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really

How is \"really well\" defined? In the domain of human auditory perception?

In this case, isn\'t \"really well\" defined as an absence of sour note(s)?

That assumes the synthesis uses the same clock as timing. I think the
discussion here has been wrt durations/intervals.

How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents (\"perfect pitch\")?

Can\'t everyone\'s ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
Perfect pitch is more than just \"naming a note\".
It\'s all but impossible for me personally to ignore the sourness of
cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
How \"sour\" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the \"previous note\" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)

https://neurosciencenews.com/pitch-detection-music-21087/

This is a reference note (middle C) followed by the same note \"soured\"
by 12 cents:

https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav

Chances are, you can\'t tell the difference hearing them
in sequence. If you heard just *one*, you\'d not be able to tell if it
was correct, or not. The third sound sample plays both simultaneously
so you can hear them beating against each other -- the difference then
becomes very noticeable!

Here\'s *one* cent difference:

https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav

And 24 cents (about the point of \"normal\" perception):

https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54

 

[John Larkin]

On Thu, 21 Jul 2022 18:21:51 +0100, Martin Brown
<\'\'\'newspam\'\'\'@nonad.co.uk> wrote:

On 21/07/2022 16:31, John Walliker wrote:
On Thursday, 21 July 2022 at 15:42:40 UTC+1, bitrex wrote:
On 7/21/2022 10:21 AM, Lasse Langwadt Christensen wrote:
torsdag den 21. juli 2022 kl. 16.04.42 UTC+2 skrev bitrex:
On 7/21/2022 7:06 AM, Martin Brown wrote:
On 21/07/2022 01:22, John Larkin wrote:
On Wed, 20 Jul 2022 19:32:20 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

John Larkin wrote:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

My system should work from a 1 PPS GPS pulse too, all boxes as
followers.

The PLL algorithm might be interesting.


It\'s certainly possible. However, within whatever tiny loop bandwidth
you wound up with, the lockers would still have

20 log(40e6) = 152 dB

higher phase noise than the lockee.

GPS has that problem too.


It would be interesting to do the math to see whether it\'s possible to
generate a concensus lock for the group: if you get everybody close
enough, just sum their sine wave outputs and lock each one of them to
that, with some bit of AC coupling or something so that they don\'t all
wander together off to the edge of the tuning range.

Maybe have one doing the locking with a phase shifter and the others
with VCOs, or something like that.

Definitely a partly-baked idea, but surely one could do better than
152 dB!

Cheers

Phil Hobbs

Each box is basically a multichannel power supply, but channels can be
programmed to do stuff in timed sequences. I want different box
outputs to time align within, say, one millisecond longterm once
programs are kicked off together. So, many microseconds of equivalent
RMS phase noise is OK as long as we stay time aligned longterm.

You really need to define longterm before the problem becomes well
posed. Do you mean hours, days, weeks or months of runtime?

Yeah I don\'t quite get it, either. My rack of synthesizers can each play
one voice of the Maple Leaf Rag via MIDI and they all stay synced
together really well, at least over a timespan of several
minutes.

but they are anot free runnign are they? they are all reacting to midi

There\'s a system clock in each one surely but they don\'t try to sync
their system clocks, they receive an instruction \"do X for Y ms\" and
their processor figures out how long Y ms is, and does it for that long.

It is literally good enough for rock & roll, but whether it\'s good
enough for power supply sequencing IDK, there is gonna be some latency.

HP used to have GPIB on their power supplies, I\'ve never used it but I
expect it wasn\'t really useful for tight synchronization.

The Group Execute Trigger command does allow quite tight synchronisation
between different GPIB devices.

GPIB flat out on a good day could manage 1Mbyte/s but in real world
situations with interconnect cabling you would be lucky to get 500kb/s.
It\'s best feature was that it ran at the maximum speed the receiving
device could handle (assuming that the controller was fast enough).

Synchronisation to a GET command would be probably be better than 1us
but would depend on the decoding time in each individual box. Some GPIB
devices were rather pedestrian at accepting commands.

IEEE488 was good in its day but a bit long in the tooth now. Still on
some test equipment in service today and was provided as standard on NEC
9801 PC\'s in Japan although hardly ever used by their customers.

Ever read the actual 488 spec? There is a state diagram that could
wreck your sleep for a week.

488 has a hardware \"accepted\" line, but for some reason SCPI in other
contexts is send-and-pray.

488 is rare on new instruments, which are ethernet and USB. A Rigol
scope makes a great USB power supply for fans and charging phones.

The cables and connectors could only be described as a bit clunky!
They really didn\'t get on with metal swarf being around but were OK in
clean dry electronics/physics labs - much less so in chemistry ones...

 

[John Larkin]

On Fri, 22 Jul 2022 16:41:40 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 06:20:58 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 00:08:56 -0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Thu, 21 Jul 2022 07:43:18 +0200, Gerhard Hoffmann <dk4xp@arcor.de
wrote:

Am 21.07.22 um 01:20 schrieb John Larkin:


Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

I have a backburner project of locking 16 MTI-260 oscillators
slooowy to another one, and when they are in sync, combine
them with an array of Wilkinsons. That should have a nice
effect on phase noise by averaging over 16.
The CPLD has enough resources to implement that as a delay
locked loop with 1 pps, but low hanging fruit first.


I could call one the leader (not \"master\") and make the others
followers (not \"slaves\") and have the leader make an active low pulse
maybe once a second. A follower would use her (not \"his\") clock to
measure the incoming period and tweak its local VCXO in the right
direction. That should work.

Don\'t GPS receivers lock their 10 MHz oscillators to a 1 PPS pulse
from the satellites?

No. There is no 1PPS pulse from the sat nor the need for exactly 10 MHz.
The sats transmit a pseudo noise sequence that is
aligned to the second of their local clock source.
The GPS receiver knows the polynomial and runs a local copy of
the polynomial. It knows by cross correlation if the local
pseudo noise is the same as that of the sat and therefore knows
the start of the second. Usually that won\'t be the case.
Then the receiver delays its own polynomial by omitting a
clock to the shift register that generates it and tries again.
Sooner or later it will fit.

Where does the 10 MHz come from?

https://en.wikipedia.org/wiki/GPS_disciplined_oscillator

\"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop.\"

That\'s what I meant: the 10M xo is locked to the 1 PPS GPS output.

The GPS 1 PPS is perfect (by definition) long-term but terrible
short-term, so the XO or rubidium has to be very good itself, and the
loop has to be very slow. Big flywheel.

GPS timing isn\'t completely perfect in reality. Antennas blow off roofs,
contractors cut cables etc. Even losing sync for a minute is sort of a big
deal. As you mentioned, jitter is the real problem. There are tradeoffs to
making a flywheel thats too heavy so to speak.

For really fussy stuff, one might have multiple GPS receivers and a quorum
of local 10Mhz oscillators. In fact, 10Mhz is a dinosaur relic for modern
stuff too. We\'ve got racks of 10Mhz oscillators and equipment to monitor
any phase shift between local oscillators and GPS sources. It\'s all going
to the dumpster when somebody finally notices it\'s been powered down and
forgotten about.

Fairly accurate nS resolution timing is possible in computers these days,
with the right tricks.

I triggered a scope from a very good ovenized XO and looked at the
rising edge of a rubidium. The edge looked solid, as if it was
internal triggered. Checking every 20 minutes or so, it ws slowly
creeping across the screen, at 5 ns/cm.

I believe they somehow pair the rubidium clocks with another quartz
crystal, even in those new tiny physics modules. I\'ve not had a chance to
tear apart a rubidium clock yet, or the ovenized stuff. They come in
little metal boxes, that remind me of TV tuners.

The rubidium physics/optics is noisy and nasty short-term. It usually
disciplines a very good VCO or VCOCXO. I have a schematic somewhere
around here; I\'ll look for it.

I\'ll be doing something similar, locking my 40 MHz clock to some 1 PPS
input, the difference being that I don\'t mind a few us of jitter, so I
can lock quick and crude.

Do you have to worry about fun issues like an the timestamp of a signal
being received before it was even transmitted between pieces of equipment?

It a multi-channel power supply!

You were also asking about timestamping in other posts. Not entirely sure
what you\'re upto in the end, but it might be interesting.

Trying to get multiple power supplies and loads to act together so
people can run, say, a modestly complex power sequence and load test
on some gear and loop that for days or weeks and stay coordinated.
Each box has 8 plugins, which naturally share the same timebase, but I
want to extend time coordination to multiple boxes. So, time lock
their XOs long-term, and start all the individual sequencers
simultaneously.

My customers complain about how nasty it is to organize a heap of
purchased ac and dc supplies and dummy loads and relay drivers, to
millisecond resolution, with a mess of weird interfaces.

Here\'s the basic idea. It\'s still evolving.

https://www.dropbox.com/s/5byvlk8uh9n23e3/P940_PD14np.pdf?dl=0

 

[John Larkin]

On Fri, 22 Jul 2022 16:54:07 -0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Fri, 22 Jul 2022 10:37:53 +0200, Gerhard Hoffmann <dk4xp@arcor.de
wrote:

Am 22.07.22 um 04:47 schrieb jlarkin@highlandsniptechnology.com:

Where does the 10 MHz come from?

https://en.wikipedia.org/wiki/GPS_disciplined_oscillator

\"GPSDOs typically phase-align the internal flywheel oscillator to the
GPS signal by using dividers to generate a 1PPS signal from the
reference oscillator, then phase comparing this 1PPS signal to the
GPS-generated 1PPS signal and using the phase differences to control
the local oscillator frequency in small adjustments via the tracking
loop.\"

That\'s what I meant: the 10M xo is locked to the 1 PPS GPS output.

No. The 1pps is asserted when the CPU thinks it\'s closest to
the \"right\" clockcycle. It could be off by half a cycle.
There is no need for 10 MHz, one could have chosen a nice
multiple of the desired baud rate.


Our GPS receivers output 1 PPS and 10 MHz. Argue with Wikipedia.

What he\'s trying to say is it may not be perfect 10 million cycles between
every 1PPS pulse. For most stuff, this is good enough. For the metrology
folks, using strong words like exactly or in this case \"locked\" will
always cause an argument.

No, the 1 PPS is sometimes generated by uP code, and sometimes jumps
back and forth around ticks of some other clock. It\'s like a rubidium,
ugly and nasty but long-term average excellent. I get the impression
that a GPS box that outputs 10 MHz, gets the 10M by locking to the 1
PPS.

The nasty 1 PPS is the bottom line of the GPS frequency standard.

Real stability on less-than-weeks time frames comes from the flywheel
effect of a very good 10 MHz oscillator and a very slow control loop.

Which is my problem, absolutely time locking a bunch of 40 MHz
oscillators from a 1 PPS pulse generated by, essentially, a relay
driver.

 

[Joe Gwinn]

On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen
<langwadt@fonz.dk> wrote:

fredag den 22. juli 2022 kl. 16.46.36 UTC+2 skrev Don Y:
On 7/22/2022 7:17 AM, Don wrote:
Don Y wrote:
Don wrote:
Don Y wrote:
bitrex wrote:

snip

Yeah I don\'t quite get it, either. My rack of synthesizers can each playone
voice of the Maple Leaf Rag via MIDI and they all stay synced together really

How is \"really well\" defined? In the domain of human auditory perception?

In this case, isn\'t \"really well\" defined as an absence of sour note(s)?

That assumes the synthesis uses the same clock as timing. I think the
discussion here has been wrt durations/intervals.

How sensitive are *your* ears to noticing small differences in pitch,
absence a comparative reference? Can you discern a difference of a few
cents (\"perfect pitch\")?

Can\'t everyone\'s ears (except perhaps the autistic tone-deaf and such)
hear a sour note relative to the preceding note? Do you need to name a
note (perfect pitch) in order to hear its sourness?
Perfect pitch is more than just \"naming a note\".
It\'s all but impossible for me personally to ignore the sourness of
cringeworthy, awkward note(s). Sour notes make me want to get out of
earshot.
How \"sour\" does the note have to be before it is perceptible, as such.
A cent? Two? Fifty? A semitone?? (about a 25 cents is typical for
the average, non-musician, listener to be able to detect -- without
context; i.e., if the \"previous note\" was similarly sour, your estimation
of the correctness of the following note can perceive both as correct...
like singing in an entirely different *key*!)

https://neurosciencenews.com/pitch-detection-music-21087/

This is a reference note (middle C) followed by the same note \"soured\"
by 12 cents:

https://en.wikipedia.org/wiki/File:Sines_12_cent_difference.wav

Chances are, you can\'t tell the difference hearing them
in sequence. If you heard just *one*, you\'d not be able to tell if it
was correct, or not. The third sound sample plays both simultaneously
so you can hear them beating against each other -- the difference then
becomes very noticeable!

Here\'s *one* cent difference:

https://en.wikipedia.org/wiki/File:Sines_1_cent_difference.wav

And 24 cents (about the point of \"normal\" perception):

https://en.wikipedia.org/wiki/File:Sines_24_cent_difference.wav

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54

My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.

This is discussed a lot in the computer music literature.

Joe Gwinn

 

[Joe Gwinn]

On Thu, 21 Jul 2022 04:17:14 -0700, jlarkin@highlandsniptechnology.com
wrote:

On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whit3rd@gmail.com
wrote:

On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down counter
to generate a correction voltage for each non-leading VCO?

It\'s actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal
events, based on its local VCO, and then do successive early/late
comparisons to the external pulses. And trim its VCXO accordingly.

Yes, exactly. And the drift between two reasonably good clocks is
slow, so the correction need not and should not be all that fast.

What I\'ve done in real applications is to periodically measure the
offset between when the external 1PPS is predicted to happen and when
it actually does, and adjust the VCO frequency such that in say 50
seconds of roughly linear convergence they will coincide (and keep on
going). The process is repeated every few seconds (exact interval not
important as it is measured).

This is roughly the algorithm a helmsman uses while steering a
sailboat, where effect is very much delayed from action.

In many computer systems it is quite difficult to do anything on a
strict time mark, but easy to measure that actual elapsed time, using
the actual clock that is being steered - it all still converges, so
long as one doesn\'t try too hard.

So, in your example, the local clock would come from a 40 MHz VCO of
good manufacture (probably needs to be a TCXO of some sort). The 40
MHz output would be fed to a divider that puts out a 1PPS pulse train.

During initialization, when the first external 1PPS leading edge is
received, reset the divider, and start counting 40 MHz cycles. Maybe
wait for things to stabilize.

Thereafter, measure signed offset between external and internal 1PPS
leading edges, and compute how much change (plus or minus) in current
VCO frequency is required for zero offset to occur in say 50 seconds
(make this time-to-zero an adjustable parameter), and change the VCO
control voltage accordingly.

A few seconds later (also an adjustable parameter), repeat the above
adjustment process, again looking 50 seconds into the future from now.
Repeat forever.

Steering to within one microsecond should be easy. Any number of
units can be following this external 1PPS signal without knowing that
one another even exist.

Beware of one thing: The 1PPS coax output from many GPS receivers is
designed to drive a 50-ohm *resistor*, not a 50-ohm transmission line.
You may need a 3dB pad right at the GPS Receiver chassis between 1PPS
output and coaxial cable to get sharp leading edges at the far end of
the coaxial cable. The classic symptom of trouble is when an o\'scope
cannot sync reliably to the 1PPS.

Also, I\'d lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.

Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.

Joe Gwinn

 

[Don Y]

On 7/22/2022 10:03 AM, John Walliker wrote:

There is cross-correlation between left and right ears in the brainstem which
is involved in determining the direction of sound sources. Detectable time
differences are remarkably small. (I would have to look it up to give a number.)

Direction (as well as elevation) is primarily determined by time differences
(Interaural Time Differences -- ITDs) and intensity differences (IIDs) as
the head casts an auditory \"shadow\" on the \"far\" ear. The shadow attenuates
higher frequencies, more. So, the brain localizes different types of sound
(frequency ranges) with different mechanisms (low frequencies exhibit less
attenuation but have longer periods in which to detect phase differences, etc.)

[There\'s considerable study on this in improving detection of emergency
vehicle \"sirens\" by altering the content of said siren to facilitate
this human process]

The \"wearer\'s\" <grin> pinnae further shape the frequency response so
each *individual* can further refine their notion of left/right, front/back,
up/down. This is highly \"wearer specific\", though.

Additionally, the presence of reflective surfaces gives multipath information
to the listener; one perceives sound differently in open space than in
an enclosed room. For repetitive sounds, you can often find folks turning or
tilting their heads to better localize the source.

You can manipulate the sounds delivered to each ear (via headphones) and
simulate the direction of a source, to some degree. I use this \"spatializer\"
effect to differentiate between different message types delivered to a
user -- a female voice off to the left might issue reminders while a
male voice to the right issues error messages -- both while a \"chosen voice\"
dead ahad provides primary narration.

[\"Voices\" can also be replaced by \"annunciators\". So, a chime off to
one side can be \"registered\" as having a particular meaning without
drawing the user\'s attention away from the narrative. Empirically,
it seems that folks can remember said events, even if one-shots,
more than they can remember sequences of sound that is otherwise devoid
of message]

 

[Don]

Joe Gwinn wrote:

<snip>

Also, I\'d lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.

Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.

This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what\'s the
\"catch\" with TP? Where\'s the \"gotcha\" to make TP harder than BNC?

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

 

[Don Y]

On 7/22/2022 1:01 PM, Joe Gwinn wrote:

On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen
langwadt@fonz.dk> wrote:

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54

Note context of post...

My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.

This is discussed a lot in the computer music literature.

Things get \"painful\" at about 50ms. I suspect your brain tries to
consider them as different events instead of indistinguishable.

 

[Don Y]

On 7/22/2022 9:02 AM, Don wrote:

Don Y wrote:

In the context of this thread, it likely has an impact. A cent is
about 500PPM (though in the frequency domain)

Your question about a one cent following note difference perception is
interesting. And, it needs to be followed up by me, so to speak.
For some unknown reason, the only thing to truly satisfy me is to
tune instruments by ear.

You\'re lucky if you can do so -- to the extent the artist(s) trust(s)
your results.

I simply want \"correct\" -- by whatever expedient gets me there, quickest!

 

[Joe Gwinn]

On Fri, 22 Jul 2022 21:38:39 -0000 (UTC), \"Don\" <g@crcomp.net> wrote:

Joe Gwinn wrote:

snip

Also, I\'d lose the BNC connectors. Threaded connectors like SMA, TNC,
and Type N are far better.

Or use shielded twisted pair to carry the 1PPS pulses. This would
work better over a backplane.

This is good advice. Even though the lazy guy within me never truly
gives up his fight to take the easy way out with BNC.
Twisted pair (TP) sounds even easier than BNC. So, what\'s the
\"catch\" with TP? Where\'s the \"gotcha\" to make TP harder than BNC?

Depends on what you are trying to do.

For nanosecond edges, coax is pretty useful, but short range and often
mechanically awkward.

For microsecond edges at 1000 meters, RS422 over shielded twisted pair
is pretty good.

For bus length links, LVDS or the like.

And so on. And there is always optical links.

Joe Gwinn

 

[Lasse Langwadt Christensen]

fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:

On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54
Note context of post...
My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.

This is discussed a lot in the computer music literature.
Things get \"painful\" at about 50ms. I suspect your brain tries to
consider them as different events instead of indistinguishable.

afaiu the limit for a phone system is >25ms round trip before you need echo canceling

 

[Don Y]

On 7/22/2022 4:52 PM, Lasse Langwadt Christensen wrote:

fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54
Note context of post...
My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.

This is discussed a lot in the computer music literature.
Things get \"painful\" at about 50ms. I suspect your brain tries to
consider them as different events instead of indistinguishable.

afaiu the limit for a phone system is >25ms round trip before you need echo canceling

Yes, but that addresses quality. A phone is still usable with
noticeable echo, esp if the echo is many dB down.

It seems like the brain has some (temporal) threshold beyond which it
can no longer treat things as being concurrent and starts a new \"recognition
process\" (so to speak) to deal with the \"other\" event.

E.g., audible feedback on a keypress that is \"too late\" is more than
just annoying; it impacts how you interact with that device.

Audio out of sync with video also has an oversized impact on
your tolerance for the information channel(s). (*Why* do we care if
the lips are out of sync with the sound? It\'s more than just
irritating...)

 

[Lasse Langwadt Christensen]

fredag den 22. juli 2022 kl. 22.37.08 UTC+2 skrev Joe Gwinn:

On Thu, 21 Jul 2022 04:17:14 -0700, jla...@highlandsniptechnology.com
wrote:

On Wed, 20 Jul 2022 23:49:40 -0700 (PDT), whit3rd <whi...@gmail.com
wrote:

On Wednesday, July 20, 2022 at 4:21:08 PM UTC-7, John Larkin wrote:
Suppose I have several rackmount boxes and each has a BNC connector on
the back. Each of them has an open-drain mosfet, a weak pullup, and a
lowpass filtered schmitt gate back into our FPGA.

I can daisy-chain several boxes with BNC cables and tees.

Each box has a 40 MHz VCXO and I want to phase-lock them, or at least
time-align them to always be the same within a few microseconds,
longterm.

If you can tolerate \'a few microseconds\' on a 40 MHz signal, that\'s not a phase-lock
problem, it\'s a frequency-lock problem. Why not just run an up/down counter
to generate a correction voltage for each non-leading VCO?

It\'s actually a time lock problem. If a follower box starts up and
sees its first 1 PPS input, it can thereafter declare 1 PPS internal
events, based on its local VCO, and then do successive early/late
comparisons to the external pulses. And trim its VCXO accordingly.

Yes, exactly. And the drift between two reasonably good clocks is
slow, so the correction need not and should not be all that fast.

What I\'ve done in real applications is to periodically measure the
offset between when the external 1PPS is predicted to happen and when
it actually does, and adjust the VCO frequency such that in say 50
seconds of roughly linear convergence they will coincide (and keep on
going). The process is repeated every few seconds (exact interval not
important as it is measured).

This is roughly the algorithm a helmsman uses while steering a
sailboat, where effect is very much delayed from action.

In many computer systems it is quite difficult to do anything on a
strict time mark, but easy to measure that actual elapsed time, using
the actual clock that is being steered - it all still converges, so
long as one doesn\'t try too hard.

So, in your example, the local clock would come from a 40 MHz VCO of
good manufacture (probably needs to be a TCXO of some sort). The 40
MHz output would be fed to a divider that puts out a 1PPS pulse train.

During initialization, when the first external 1PPS leading edge is
received, reset the divider, and start counting 40 MHz cycles. Maybe
wait for things to stabilize.

Thereafter, measure signed offset between external and internal 1PPS
leading edges, and compute how much change (plus or minus) in current
VCO frequency is required for zero offset to occur in say 50 seconds
(make this time-to-zero an adjustable parameter), and change the VCO
control voltage accordingly.

A few seconds later (also an adjustable parameter), repeat the above
adjustment process, again looking 50 seconds into the future from now.
Repeat forever.

isn\'t that kind how NTP works?, speeding up or slowing down over some period
to sync time with the server without big jumps and always increasing (except possibly at start up)

come to think of it, some closed loop servo systems (and step generators) for things like CNC machine work similarly
at a fixed interval, say a few kHz, current target and actual position is compared, from that (usually with a PI loop)
the speed of the motor (or frequency of steps) is set so the position will hit the next target at the next timer tick

 

[Lasse Langwadt Christensen]

lørdag den 23. juli 2022 kl. 02.10.41 UTC+2 skrev Don Y:

On 7/22/2022 4:52 PM, Lasse Langwadt Christensen wrote:
fredag den 22. juli 2022 kl. 23.44.07 UTC+2 skrev Don Y:
On 7/22/2022 1:01 PM, Joe Gwinn wrote:
On Fri, 22 Jul 2022 10:54:30 -0700 (PDT), Lasse Langwadt Christensen
lang...@fonz.dk> wrote:

If your device\'s *timing* was off by 0.05%, would that be consequential?

https://youtu.be/AFaRIW-wZlw?t=54
Note context of post...
My recollection is the for a chorus to be in unison, all the singers
must be within twenty milliseconds of one another.

This is discussed a lot in the computer music literature.
Things get \"painful\" at about 50ms. I suspect your brain tries to
consider them as different events instead of indistinguishable.

afaiu the limit for a phone system is >25ms round trip before you need echo canceling
Yes, but that addresses quality. A phone is still usable with
noticeable echo, esp if the echo is many dB down.

sure, but it seems that below ~25ms it is not noticable

It seems like the brain has some (temporal) threshold beyond which it
can no longer treat things as being concurrent and starts a new \"recognition
process\" (so to speak) to deal with the \"other\" event.

at big concerts with speaker towers for the people far away from the stage
those speakers gets delayed so they are 10-15ms behind the sound from the stage
giving the illusion that all the sound is from the main Pa at the stage