aLaw module works strangely in miniDSP of aic3254

Oleg Yurchenko

Sorry for my english...

Hi, I attempting to solve next task:

Receiving audio data from AIC3254 with alaw compression in miniDSP. I create the next scheme in PPS:

That is correct?

Next, I connect to mic_in the signal from the native sound card of my computer and write wav file (my settings - 16 KHz 16 bit). But I receive the next picture:

I'm confused with this. For example, _F935 -> 7FFF_ and _04B1->8000_. I'm not understand why.

After that I try to compress this file to alaw format by other program, and I get next results:

For example, _7FFF -> AA_ , _F935 -> 6E_, _8000->2A_ and _04B1->96_. This is correct... but why the data from alaw module (from miniDSP) isn't correct?

I will be grateful for all the tips..

over 10 years ago

0 Don Dapkus over 10 years ago

TI__Guru**** 189399 points

Hi, Oleg,

I'm not sure how much we can help you with this, but I've asked my colleague to comment on your post.

-d2

0 Dominik Hartl11 over 10 years ago

TI__Guru 51466 points

What is the result if you run the left channel data through an a-law decoder on your PC?

0 Oleg Yurchenko over 10 years ago in reply to Dominik Hartl11

Intellectual 330 points

D. Hartl, thanks for reply.

I insert an a-law decoder in my scheme, and I get the next table:

0 Oleg Yurchenko over 10 years ago in reply to Dominik Hartl11

Intellectual 330 points

My experiments give next result:

When I turn off signal on input, I get the same result with 0x7FFF. I use the scheme that has been proposed on the forum:

Why it isn't work?

0 Oleg Yurchenko over 10 years ago in reply to Dominik Hartl11

Intellectual 330 points

I have an assumption that the data I have received could be distorted. Distortion could be introduced at the stage when the computer program will adjust the gain in a compressed audio channel.

There is another question. How often need to load factors and instructions miniDSP (on my board by MSP430)? Once or at each power-on sequence?

0 Dominik Hartl11 over 10 years ago in reply to Oleg Yurchenko

TI__Guru 51466 points

You'll have to load the miniDSP program and data after each reset/power cycle.

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aLaw module works strangely in miniDSP of aic3254