Instantaneous (analogue) compression of speech signals

John Woodgate · Jan 3, 2005

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals? I've been doing a
little work on it but I'm unable to judge the resulting sound quality.
Why do treble boost controls no longer have any audible effect for me?
(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Jim Thompson · Jan 3, 2005

On Mon, 3 Jan 2005 21:21:14 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals? I've been doing a
little work on it but I'm unable to judge the resulting sound quality.
Why do treble boost controls no longer have any audible effect for me?
(;-)

480)460-2350 | |
| E-mail Address at Website Fax

Rich Grise · Jan 3, 2005

On Mon, 03 Jan 2005 21:21:14 +0000, John Woodgate wrote:

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals?

Intentionally? ;-)

I've been doing a
little work on it but I'm unable to judge the resulting sound quality.

Well, isn't that a pretty good indication that your clipper isn't
introducing objectionable distortion? ;-) With speech, AIUI, you can do a
dramatic amount of clipping (10 dB? 20 dB? I read it in some Ham
magazine article mumble years ago) and still be intelligible. And the only
thing soft about it is an ordinary silicon knee; that's about all the
softness you really need, with speech.

Why do treble boost controls no longer have any audible effect for me?
(;-)

Too much Twisted Sister at volume level 11 in your misspent youth? ;-P

Cheers!
Rich

Adrian Jansen · Jan 3, 2005

John Woodgate wrote:

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals? I've been doing a
little work on it but I'm unable to judge the resulting sound quality.
Why do treble boost controls no longer have any audible effect for me?
(;-)
Back in the ancient days of 27MHz CB radios there was heaps of work done

on compression and clipping to get the most "voice power" onto the
carrier. Is that the sort of compression you want ?

Your ears, like mine, probably date from this period too, if you cant
hear treble anymore

--
Regards,

Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.

gwhite · Jan 4, 2005

John Woodgate wrote:

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals?

What the hell is "soft clipping?" It sounds like "golden ears" audiophile
mumbo-jumbo.

I've been doing a
little work on it but I'm unable to judge the resulting sound quality.
Why do treble boost controls no longer have any audible effect for me?
(;-)

Hey, the bright side is you don't have to spend any money on components to boost
the bright side.

Jim Thompson · Jan 4, 2005

On Tue, 04 Jan 2005 02:38:07 GMT, gwhite <gwhite@ti.com> wrote:

John Woodgate wrote:

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals?

What the hell is "soft clipping?" It sounds like "golden ears" audiophile
mumbo-jumbo.

[snip]

480)460-2350 | |
| E-mail Address at Website Fax

John Woodgate · Jan 4, 2005

I read in sci.electronics.design that Rich Grise <richgrise@example.net>
wrote (in <pan.2005.01.03.22.37.33.248842@example.net&gt

about
'Instantaneous (analogue) compression of speech signals', on Mon, 3 Jan
2005:

On Mon, 03 Jan 2005 21:21:14 +0000, John Woodgate wrote:

Why do treble boost controls no longer have any audible effect for me?
(;-)

Too much Twisted Sister at volume level 11 in your misspent youth? ;-P

You have determined the problem, but the cause is idiopathic and

familial. My misspent youth dates from just after Greensleeves was top-
of-the-pops. (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

John Woodgate · Jan 4, 2005

I read in sci.electronics.design that Adrian Jansen <adrian@qq.vv.net>
wrote (in <41d9c802$1@duster.adelaide.on.net&gt

about 'Instantaneous
(analogue) compression of speech signals', on Tue, 4 Jan 2005:

Back in the ancient days of 27MHz CB radios there was heaps of work done
on compression and clipping to get the most "voice power" onto the
carrier. Is that the sort of compression you want ?

Yes, and low-cost. FFT and DSP solutions are unlikely to be justifiable
on a cost/benefit basis, but a couple of diodes and a quad op-amp is a
different matter.

Your ears, like mine, probably date from this period too, if you cant
hear treble anymore

Indeed.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Anthony C Smith · Jan 4, 2005

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:g2$9LkCwPk2BFwoE@jmwa.demon.co.uk...

I read in sci.electronics.design that gwhite <gwhite@ti.com> wrote (in
41DA01BB.40D3FCC1@ti.com&gt about 'Instantaneous (analogue) compression
of speech signals', on Tue, 4 Jan 2005:
John Woodgate wrote:
John- a very good soft clipper can be formed by placing a pair of back to

back zeners in parallel with the feedback resistor on an opamp- the leakage
from the zeners brakes the signal slowly before the Vz+0.7 point- this
increases the THD on even harmonics only and sounds OK in practice - if you
want a better limiter a fet and rectifier would be the way to go but more
complex.
regards
Anthony

martin griffith · Jan 4, 2005

On Tue, 4 Jan 2005 07:12:59 +0000, in sci.electronics.design John
Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Adrian Jansen <adrian@qq.vv.net
wrote (in <41d9c802$1@duster.adelaide.on.net&gt about 'Instantaneous
(analogue) compression of speech signals', on Tue, 4 Jan 2005:

Back in the ancient days of 27MHz CB radios there was heaps of work done
on compression and clipping to get the most "voice power" onto the
carrier. Is that the sort of compression you want ?

Yes, and low-cost. FFT and DSP solutions are unlikely to be justifiable
on a cost/benefit basis, but a couple of diodes and a quad op-amp is a
different matter.

Your ears, like mine, probably date from this period too, if you cant
hear treble anymore

Indeed.
Hi John,

have a look at alesis semiconductor/aka wavefront semi available from
profusion. They do a very cheep DSP, AL3101 IIRC, less than a fiver,
that is designed for this sort of thing. There is a Perl based
complier for it somewhere as well, freeware

martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

Keith Wootten · Jan 4, 2005

In message <2pRIs3CKdb2BFwac@jmwa.demon.co.uk>, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> writes

Does anyone here have any experience of instantaneous (analogue)
compression (aka soft clipping) of speech signals? I've been doing a
little work on it but I'm unable to judge the resulting sound quality.
Why do treble boost controls no longer have any audible effect for me?
(;-)

Howzabout a potential divider with the top leg being a small
incandescent lamp. Also acts as an emergency beacon where the louder
you call for help, the brighter is the lamp.

Wayne Bridges is the expert with this method of course.

Cheers
--
Keith Wootten

Anthony C Smith · Jan 4, 2005

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:3VCIT$EG+m2BFwp6@jmwa.demon.co.uk...
_snip-

Thanks for that. Are you sure it's even harmonics? If the clipping is
precisely symmetrical the harmonics are all odd order.
Good point now i look at it- I used this method with a pair of 3v3 zeners in

parallel with a 10K feedback resistor on a TL072 (2k2 Rin) and the even
harmonics increased IIRC when viewed with FFT analyser on my AP- still the
ears test is the best and it sounds OK when used on a mic preamp- limiting
starts around 2.6V and still has round corners when you hit the limit at 4V
(peak) ie no sharp transistion from the rising of the sine wave and the clip
point line.
simplest is to try it and see- its simple enough-
regards
Anthony

Jim Thompson · Jan 4, 2005

On Tue, 4 Jan 2005 19:26:44 +0000 (UTC), "Reg Edwards"
<g4fgq.regp@ZZZbtinternet.com> wrote:

Digital stuff is just a passing fashion.

ANALOGUE INEVITABLY RULES!

You can't design a microprocessor without considering the inter-connections
to be transmission lines with Zo, attenuation and phase delay.

480)460-2350 | |
| E-mail Address at Website Fax

Reg Edwards · Jan 4, 2005

Digital stuff is just a passing fashion.

ANALOGUE INEVITABLY RULES!

You can't design a microprocessor without considering the inter-connections
to be transmission lines with Zo, attenuation and phase delay.

Rob Gaddi · Jan 4, 2005

John Woodgate wrote:

DSP may be over the top, but a PIC (or
whatever) with ADC, look-up table and DAC would be pretty simple for a
Lo-Fi implementation.

True, but anything like that raises EMC issues, which I don't want to
get involved in. Analogue is much less hassle, if it works well enough.

Not too too badly. TI's MSP430 line pulls less than 2mA and doesn't
need an external clock. I haven't read up specifically on any of the
EMC issues, but with no loops or high currents it's hard to see what
would broadcast.

Ken Smith · Jan 5, 2005

In article <n7olt0pimqncoidcohk7mi2jgs8jsjfa82@4ax.com>,
Jim Thompson <thegreatone@example.com> wrote:
[...]

How about "compandors" used by most radio stations to keep their
modulation index maxed out....

I like the homomorphic compressor, not because it is better in any way but
because it is unusual.

Take the abs() of the signal but remember the sign.

Take the ln() of the abs()

High pass

do the exp()

Restore the sign.

--
--
kensmith@rahul.net forging knowledge

Pig Bladder · Jan 5, 2005

On Tue, 04 Jan 2005 17:45:36 +0000, John Woodgate wrote:

I read in sci.electronics.design that Roger Hamlett <rogerspamignored@tt

everything above about 2.5Khz, and still understand speech perfectly),
but would massively reduce the effect of treble 'boost' controls.

Yes, you've twigged it. I have lost a lot from 1 kHz up and that does
cause problems with speech.

You're trying to build a hearing aid, without admitting that you need a
hearing aid, is this it?
--
The Pig Bladder From Uranus, Still Waiting for
Some Hot Babe to Ask What My Favorite Planet Is.

budgie · Jan 5, 2005

On Wed, 5 Jan 2005 07:48:52 +0000, John Woodgate <jmw@jmwa.demon.contraspam.yuk>
wrote:

No, I have hearing aids and I make no secret of them. What I'm doing is
about:

- the effects of (non-linear) signal degradations on speech
intelligibility;

- the anomaly that some 'degradations' actually increase
intelligibility.

John, have you looked at the circuits used in commercial two-way radio
equipment? It varies from some pretty harsh diode types (with predictably high
output distortion) to some which do have the effect of improved "effectiveness"
through a better (output) average-to-peak ratio. If it will help (it's a bit
hard to actually describe the circuit) I could send you a scan of the relevant
part from one type that we found surpisingly good when overdriven by a large
margin.

Ric · Jan 5, 2005

John Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Rich Grise <richgrise@example.net
wrote (in <pan.2005.01.05.04.17.15.238991@example.net&gt about
'Instantaneous (analogue) compression of speech signals', on Wed, 5 Jan
2005:

If a diode clipper is unsatisfactory, would a log amp do?

Not directly, because of the problem with negative-going half-cycles.

What about a "true" log amp (aka Log Video)? These have a sort of
S-shaped response that's symmetrical about 0V.

--
Rick

Nico Coesel · Jan 5, 2005

John Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Adrian Jansen <adrian@qq.vv.net
wrote (in <41d9c802$1@duster.adelaide.on.net&gt about 'Instantaneous
(analogue) compression of speech signals', on Tue, 4 Jan 2005:

Back in the ancient days of 27MHz CB radios there was heaps of work done
on compression and clipping to get the most "voice power" onto the
carrier. Is that the sort of compression you want ?

Yes, and low-cost. FFT and DSP solutions are unlikely to be justifiable
on a cost/benefit basis, but a couple of diodes and a quad op-amp is a
different matter.

In that case, use a voltage controlled amplifier and control the
voltage by the filtering the output of a peak detector. I've used
these circuits many times with excellent results.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

Instantaneous (analogue) compression of speech signals

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Jim Thompson

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