Microphone arrays and Raspberry Pi

[Tareq Matar]

this is my first project and im confused about microphones, i want to connect four electret microphones to the Raspberry Pi and i dont know where to connect them, am i supposed to use analog/digital convereters ADCs, do i have to use amplifires with them or not.

i have figured everything else but im stuck at this point, please help me

 

[Tim Wescott]

On Fri, 25 Jul 2014 15:44:02 -0700, Tareq Matar wrote:

this is my first project and im confused about microphones, i want to
connect four electret microphones to the Raspberry Pi and i dont know
where to connect them, am i supposed to use analog/digital convereters
ADCs, do i have to use amplifires with them or not.

i have figured everything else but im stuck at this point, please help
me

I _think_ you won't need much, if any, amplification to use an electret
microphone. If you do, simple op-amp circuits should work OK.

You _do_ need to use an ADC of some sort.

Does the Rasberry Pi have four analog input channels of sufficient speed,
or do you need to add them?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[David Harmon]

On Fri, 25 Jul 2014 20:02:21 -0500 in sci.electronics.basics, Tim
Wescott <tim@seemywebsite.really> wrote,

Does the Rasberry Pi have four analog input channels of sufficient speed,
or do you need to add them?

Raspberry Pi does not have any analog inputs. A USB sound adapter
could work for microphone input.

 

[Bob Masta]

On Sun, 27 Jul 2014 22:28:51 -0700, David Harmon
<source@netcom.com> wrote:

On Fri, 25 Jul 2014 20:02:21 -0500 in sci.electronics.basics, Tim
Wescott <tim@seemywebsite.really> wrote,
Does the Rasberry Pi have four analog input channels of sufficient speed,
or do you need to add them?

Raspberry Pi does not have any analog inputs. A USB sound adapter
could work for microphone input.

The FAQs say that you can add "any supported USB
microphone". That probably means mono, possibly stereo, but
certainly not 4-channel. There is at least one stereo
input audio device available from Wolfson, but I don't see
anything beyond that.

So you'll need to use an I2C device. Do a Google search for

"A/D input raspberry pi" (without the quotes) to see your
options. My quick review turned up multi-channel devices
that sampled at rather slow rates (3300 samples/sec for
example on the Adafruit 4-channel 12-bit board).

So you need to decide how low a sample rate your project can
tolerate, then see if there are any devices that can support
it. As I noted on the DPS newsgroup, the *multi-channel*
sample rate may be slower than the single-channel rate you
see in advertisements. And you'll need that rate to be much
faster than the highest frequency you want to measure.
(At least 2x, but more would be better.)

Best regards,


Bob Masta

DAQARTA v7.60
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, Pitch Track, Pitch-to-MIDI
FREE Signal Generator, DaqMusiq generator
Science with your sound card!

 

[Tareq Matar]

On Monday, 28 July 2014 15:49:23 UTC+3, Bob Masta wrote:

On Sun, 27 Jul 2014 22:28:51 -0700, David Harmon

wrote:



On Fri, 25 Jul 2014 20:02:21 -0500 in sci.electronics.basics, Tim

Wescott wrote,

Does the Rasberry Pi have four analog input channels of sufficient speed,

or do you need to add them?



Raspberry Pi does not have any analog inputs. A USB sound adapter

could work for microphone input.



The FAQs say that you can add "any supported USB

microphone". That probably means mono, possibly stereo, but

certainly not 4-channel. There is at least one stereo

input audio device available from Wolfson, but I don't see

anything beyond that.



So you'll need to use an I2C device. Do a Google search for



"A/D input raspberry pi" (without the quotes) to see your

options. My quick review turned up multi-channel devices

that sampled at rather slow rates (3300 samples/sec for

example on the Adafruit 4-channel 12-bit board).



So you need to decide how low a sample rate your project can

tolerate, then see if there are any devices that can support

it. As I noted on the DPS newsgroup, the *multi-channel*

sample rate may be slower than the single-channel rate you

see in advertisements. And you'll need that rate to be much

faster than the highest frequency you want to measure.

(At least 2x, but more would be better.)



Best regards,





Bob Masta



DAQARTA v7.60

Data AcQuisition And Real-Time Analysis

www.daqarta.com

Scope, Spectrum, Spectrogram, Sound Level Meter

Frequency Counter, Pitch Track, itch-to-MIDI

FREE Signal Generator, DaqMusiq generator

Science with your sound card!

my project requires about 8K sample/second for each channel, i couldn't find any A/D converter with that rate.
is there a way or another ADC to obtain that rate ?

 

[Maynard A. Philbrook Jr.]

article <bb9ae70d-1e07-4a0f-aa98-4822375d5432@googlegroups.com>,
tareqmatarr@gmail.com says...

Science with your sound card!

my project requires about 8K sample/second for each channel, i couldn't find any A/D converter with that rate.
is there a way or another ADC to obtain that rate ?

Can't use something like this;

http://www.adafruit.com/products/856
?

Here is another idea which requires you to use a secondary
small uC because I am sure the PI can not keep up with the
data flow, with a helper processor you can buffer up the incoming
and get packets of info in compressed form. Of course be prepared
to pay the price!

http://www.analog.com/en/audiovideo-products/audio-ad-
converters/ad1974/products/product.html

Also with example, two of these will give you 4 in and 4 0ut.

http://www.cirrus.com/en/pubs/proDatasheet/cs4220-3.pdf

Jamie