RE: Re: sound APIs/programming

Thanks for the portaudio link Darren. It looks interesting...

Here is some knowledge I've gained regarding audio input with AudioStix. (As
best I can discern, information posted from Craig has not been quite
correct, but he was probably responding from memory.)

Using aumix:

Command / UCB1400 Register / Value written

-i 100  ->  0x1c  ->  0x0f0f  =  Max input gain (whether mic or line input)
(+21.5 db)
-i 0    ->  0x1c  ->  0x8000  =  Min input gain (all mute)

-m 100  ->  0x0e  ->  0x0040  =  Mic preamp enabled (+20 dB)
-m 0    ->  0x0e  ->  0x0000  =  Mic preamp disabled

-l R    ->  0x1a  ->  0x0404  =  Select line in for recording
                                                (Stereo recording, mic preamp 
bypassed)
-m R    ->  0x1a  ->  0x0000  =  Select mic in for recording
                                                (Left mono recording, Right 
channel copied from Left)

-v 0-100  ->  Master volume control

I do not think that separate left volume/right volume control (balance) is
possible using aumix without the ncurses interface. Is that true?

Also, recording using brec should be done stereo even though the mic is
mono. Mono settings with brec will write an incorrect .wav header and only
record for 1/2 as long as requested.


This brings me back my original query about decent quality microphone
recordings.  I've been able to make reasonable recordings from line in CD
sources, but all of my attempts at microphone recordings have significant
hiss and poor gain. (Similar to the type of voice recordings one can make
with, for example, an IPAQ using the built-in mic.)

Has anyone had success making good S/N microphone recordings?

If not, my conclusion at this point is the that the preamp on the UCB1400 is
crap, or significant digital noise is creeping into the audio circuitry,
probably both.

I'm looking at using a separate battery powered mic preamp, but the smallest
I can find is bigger than gumstix and requires 9 V. :-) So much for
miniaturization....

- Seth












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