Speex dev - Aug 2006 - AEC on a TI C6x - has no effect

Itay,
>I am trying these things, but the main problem that has been bothering
>me recently is that the fixed-point algorithm works "sometimes".
Meaning
>that sometimes it will work well, and other times it will not work at
>all.
>
>I think I've found the source of the problem. The speex_alloc()
>function, called by speex_echo_state_init(), calls calloc() and returns
>a zeroed array. On the other hand, the TI implementation (as it is if
>you don't change the MANUAL_ALLOC define) replaces speex_alloc() with a
>different version that doesn't use the heap but only allocates memory
>from a large application-supplied memory block. Nothing zeroes this
>memory, and there is no hint in the comments (ti\user_misc.h, lines
>36-46) to let me know that the block must be zeroed externally. I
>believe this should be clarified in these comments, or perhaps instead
>add a memset in speex_alloc() in ti\user_misc.h to zero the memory.
>Now that I'm zeroing this block in my initialization, everything seems
>to be working much more consistently.
There IS a memset at the bottom of speex_alloc in ti\user_misc.h, so I do 
not understand why your zeroing of this block makes any difference.  There 
may be some more subtle problem.

- Jim

Jim,

You're right, the memset really is there, how could I miss that? :)

I also spoke too soon, as my change doesn't solve anything. At each run,
something random causes the algorithm to either work or not work at all.
There is a correspondence between whether the echo cancel works and
whether the st->PHI and st->W arrays contain data or zeroes. (the arrays
contain zeroes when alg fails, and data when alg works.)

I have tried running the trivial case where the canceller is given two
identical buffers, and it works every time.

The only thing that I know of that can change slightly between runs is
perhaps a minor change in the delay between the play and record buffers.
I have verified, however, that the play buffer is always ahead of the
rec buffer, so the echo canceller is always trying to cancel a signal
that it has seen before.

Can slight differences in this delay cause this problem? What could
cause the PHI and W arrays (sorry I keep calling them that, I don't know
what their meaning is) to be zeroes only?

Thanks,

-Itay

-----Original Message-----
From: Jim Crichton [mailto:jim.crichton@comcast.net] 
Sent: Thursday, August 17, 2006 2:52 PM
To: Itay Chamiel
Cc: speex-dev@xiph.org
Subject: Re: [Speex-dev] AEC on a TI C6x - has no effect

Itay,
>I am trying these things, but the main problem that has been bothering 
>me recently is that the fixed-point algorithm works "sometimes". 
>Meaning that sometimes it will work well, and other times it will not 
>work at all.
>
>I think I've found the source of the problem. The speex_alloc() 
>function, called by speex_echo_state_init(), calls calloc() and returns
>a zeroed array. On the other hand, the TI implementation (as it is if 
>you don't change the MANUAL_ALLOC define) replaces speex_alloc() with a
>different version that doesn't use the heap but only allocates memory 
>from a large application-supplied memory block. Nothing zeroes this 
>memory, and there is no hint in the comments (ti\user_misc.h, lines
>36-46) to let me know that the block must be zeroed externally. I 
>believe this should be clarified in these comments, or perhaps instead 
>add a memset in speex_alloc() in ti\user_misc.h to zero the memory.
>Now that I'm zeroing this block in my initialization, everything seems 
>to be working much more consistently.
There IS a memset at the bottom of speex_alloc in ti\user_misc.h, so I
do not understand why your zeroing of this block makes any difference.
There may be some more subtle problem.

- Jim

> I have tried running the trivial case where the canceller is given two
> identical buffers, and it works every time.
So it would indicate the code itself performs the same every time.
> The only thing that I know of that can change slightly between runs is
> perhaps a minor change in the delay between the play and record buffers.
> I have verified, however, that the play buffer is always ahead of the
> rec buffer, so the echo canceller is always trying to cancel a signal
> that it has seen before.
> 
> Can slight differences in this delay cause this problem? What could
> cause the PHI and W arrays (sorry I keep calling them that, I don't
know
> what their meaning is) to be zeroes only?
I don't know, but the only way to know would be to save the data you're
sending to the AEC. That way you'll be able to see what's going on.
There's no way to do anything when the data is different every time.
Something tells me that the problem is somewhere in your DAC/ADC
interface code.

	Jean-Marc