Speex dev - Jun 2007 - Time Delay Estimation

Here's a question that may seem strange.

Does the echo canceller maintain some data structure that I might be
able to use if I wanted to estimate the amount of delay between the
near-end and far-end signals? I'd like to be able to do this in order to
optimally align the signals before passing them to the canceller. There
seem to be many milliseconds of latency in a Wintel audio subsystem and
I would like to accurately compensate for that rather than just using a
huge echo tail.

I would guess that the adaptive filter must compute some good data that
I could use as observations for a tracking algorithm.

I would appreciate hearing about any suggestions you may have.

Thanks

> Does the echo canceller maintain some data structure that I might be
> able to use if I wanted to estimate the amount of delay between the
> near-end and far-end signals? I'd like to be able to do this in order
to
> optimally align the signals before passing them to the canceller. There
> seem to be many milliseconds of latency in a Wintel audio subsystem and
> I would like to accurately compensate for that rather than just using a
> huge echo tail.
> 
> I would guess that the adaptive filter must compute some good data that
> I could use as observations for a tracking algorithm.
If you don't need too much accuracy, you can look at the prop[] array.
The index of the largest element in "prop" will give you the delay in
frames. If you need more accurate, then you'll need to convert the
frequency-domain weights (W) tp time domain and look for the max.

	Jean-Marc

Aha. By "frames" I assume you mean 10ms or 20ms or whatever I have
passed as frame_size to speex_echo_state_init. Correct? (I suppose I
could go to a smaller frame size if desiring finer precision.)

I gather that prop[] contains proportional adaptation rates. I guess
I'll have to read up on the MDF algorithm to get a better sense of what
that means.

Thanks


-----Original Message-----
From: Jean-Marc Valin [mailto:jean-marc.valin@usherbrooke.ca] 
Sent: Thursday, June 07, 2007 4:55 PM
To: Coffey, Michael
Cc: speex-dev@xiph.org
Subject: Re: [Speex-dev] Time Delay Estimation
> Does the echo canceller maintain some data structure that I might be
> able to use if I wanted to estimate the amount of delay between the
> near-end and far-end signals? I'd like to be able to do this in order
to
> optimally align the signals before passing them to the canceller.
There
> seem to be many milliseconds of latency in a Wintel audio subsystem
and
> I would like to accurately compensate for that rather than just using
a
> huge echo tail.
> 
> I would guess that the adaptive filter must compute some good data
that
> I could use as observations for a tracking algorithm.
If you don't need too much accuracy, you can look at the prop[] array.
The index of the largest element in "prop" will give you the delay in
frames. If you need more accurate, then you'll need to convert the
frequency-domain weights (W) tp time domain and look for the max.

	Jean-Marc