| Author |
Message |
Robert Oschler
Guest
|
 Posted:
Thu Mar 31, 2005 1:28 am Post subject:
Is there an Open Source Echo Cancellation module available? |
|
|
Hello,
I am the lead programmer for the SourceForge based Robosapien Dance Machine
project, released under the GPL license:
http://sourceforge.net/projects/robodance
I just added voice recognition capability to the program using another
SourceForge open source project, the Sphinx 3.5 speech recognition engine:
http://sourceforge.net/projects/cmusphinx
The Robosapien robot is a very loud robot which, using the average speech
detection/silence detection algorithms, will trigger a lot of "false"
recognition activity on the microphone; even on a decent headset microphone.
At about 3 feet away he still pumps out healthy 60+ decibels of sound which
left unchecked, triggers the microphone frequently and subsequently
generating false recognition results.
I managed to do a very effective job at eliminating the problem using some
tricky volume thresholding, but in the future I'd like to go a step further
and use echo cancellation techniques to remove the robot's "voice".
It would be very simple for me to record everything the robot says, each to
separate audio file. Since my program is controlling the robot, I always
know exactly what he is saying. Therefore, I should be able to take the
appropriate pre-recorded audio file of his voice and remove it from the
incoming microphone signal using spectral subtraction techniques.
But since I am not a DSP expert (that's an understatement), I'd be far
better off finding some open source code that I could include in the project
to perform the spectral subtraction.
I'd need the module to be able to take a pre-recorded file and create a
filter that would remove the audio in that file, from an audio signal in
real-time (live microphone input). I would need that filter to be able to
adapt to differences between the audio contained in the pre-recorded file,
and the way that audio will sound coming in on a different microphone than
the one the audio was originally recorded with, and at a different distance
from the microphone as the original (pre-recorded file versus actual audio
coming in from a new microphone).
Does anyone know of something I could use? I am a veteran, C/C++/Object
Pascal programmer and can even handle some assembler if needed.
Thank you if you have read this far, I know it's a long message. :)
Thanks,
--
Thanks,
Robert
http://www.evosapien.com/
Robosapien Hacks & Tricks |
|
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|
 |
Jerry Avins
Guest
|
| Posted:
Thu Mar 31, 2005 4:03 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
Robert Oschler wrote:
| Quote: | Hello,
I am the lead programmer for the SourceForge based Robosapien Dance Machine
project, released under the GPL license:
http://sourceforge.net/projects/robodance
I just added voice recognition capability to the program using another
SourceForge open source project, the Sphinx 3.5 speech recognition engine:
http://sourceforge.net/projects/cmusphinx
The Robosapien robot is a very loud robot which, using the average speech
detection/silence detection algorithms, will trigger a lot of "false"
recognition activity on the microphone; even on a decent headset microphone.
At about 3 feet away he still pumps out healthy 60+ decibels of sound which
left unchecked, triggers the microphone frequently and subsequently
generating false recognition results.
I managed to do a very effective job at eliminating the problem using some
tricky volume thresholding, but in the future I'd like to go a step further
and use echo cancellation techniques to remove the robot's "voice".
It would be very simple for me to record everything the robot says, each to
separate audio file. Since my program is controlling the robot, I always
know exactly what he is saying. Therefore, I should be able to take the
appropriate pre-recorded audio file of his voice and remove it from the
incoming microphone signal using spectral subtraction techniques.
But since I am not a DSP expert (that's an understatement), I'd be far
better off finding some open source code that I could include in the project
to perform the spectral subtraction.
I'd need the module to be able to take a pre-recorded file and create a
filter that would remove the audio in that file, from an audio signal in
real-time (live microphone input). I would need that filter to be able to
adapt to differences between the audio contained in the pre-recorded file,
and the way that audio will sound coming in on a different microphone than
the one the audio was originally recorded with, and at a different distance
from the microphone as the original (pre-recorded file versus actual audio
coming in from a new microphone).
Does anyone know of something I could use? I am a veteran, C/C++/Object
Pascal programmer and can even handle some assembler if needed.
Thank you if you have read this far, I know it's a long message. :)
Thanks,
|
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
Lets take a different scenario. You have two microphones in a room and a
speaker who is not always in the same place. The microphones, although
the same model, are not identical; nor do they receive precisely the
same acoustic signal. What would need to happen in order for the output
of one of them to cancel the other's?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
|
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|
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Jon Harris
Guest
|
| Posted:
Thu Mar 31, 2005 4:38 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
What is the relationship between the robot's loudspeaker and the microphone? Is
it fixed or dynamic? I'm guessing the microphone is fixed but the robot's
loudspeaker is going to be moving. This makes it harder for an adaptive
algorithm to work well as it is constantly having to adapt.
My first thought would be a much simpler solution: turn off speech recognition
while that loud robot is "talking"!
FWIW, I don't know of any open source echo cancellation code. I'm aware of a
few commercial products.
"Robert Oschler" <no-mail-please@nospam.com> wrote in message
news:gsGdnb7MOfFGl9bfRVn-hw@adelphia.com...
| Quote: | Hello,
I am the lead programmer for the SourceForge based Robosapien Dance Machine
project, released under the GPL license:
http://sourceforge.net/projects/robodance
I just added voice recognition capability to the program using another
SourceForge open source project, the Sphinx 3.5 speech recognition engine:
http://sourceforge.net/projects/cmusphinx
The Robosapien robot is a very loud robot which, using the average speech
detection/silence detection algorithms, will trigger a lot of "false"
recognition activity on the microphone; even on a decent headset microphone.
At about 3 feet away he still pumps out healthy 60+ decibels of sound which
left unchecked, triggers the microphone frequently and subsequently
generating false recognition results.
I managed to do a very effective job at eliminating the problem using some
tricky volume thresholding, but in the future I'd like to go a step further
and use echo cancellation techniques to remove the robot's "voice".
It would be very simple for me to record everything the robot says, each to
separate audio file. Since my program is controlling the robot, I always
know exactly what he is saying. Therefore, I should be able to take the
appropriate pre-recorded audio file of his voice and remove it from the
incoming microphone signal using spectral subtraction techniques.
But since I am not a DSP expert (that's an understatement), I'd be far
better off finding some open source code that I could include in the project
to perform the spectral subtraction.
I'd need the module to be able to take a pre-recorded file and create a
filter that would remove the audio in that file, from an audio signal in
real-time (live microphone input). I would need that filter to be able to
adapt to differences between the audio contained in the pre-recorded file,
and the way that audio will sound coming in on a different microphone than
the one the audio was originally recorded with, and at a different distance
from the microphone as the original (pre-recorded file versus actual audio
coming in from a new microphone).
Does anyone know of something I could use? I am a veteran, C/C++/Object
Pascal programmer and can even handle some assembler if needed.
Thank you if you have read this far, I know it's a long message. :)
Thanks,
--
Thanks,
Robert
http://www.evosapien.com/
Robosapien Hacks & Tricks
|
|
|
| Back to top |
|
|
Robert Oschler
Guest
|
| Posted:
Thu Mar 31, 2005 6:56 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Jon Harris" <goldentully@hotmail.com> wrote in message
news:3b0rgnF6d12jsU1@individual.net...
| Quote: | What is the relationship between the robot's loudspeaker and the
microphone? Is
it fixed or dynamic? I'm guessing the microphone is fixed but the robot's
loudspeaker is going to be moving. This makes it harder for an adaptive
algorithm to work well as it is constantly having to adapt.
My first thought would be a much simpler solution: turn off speech
recognition
while that loud robot is "talking"!
FWIW, I don't know of any open source echo cancellation code. I'm aware
of a
few commercial products.
"Robert Oschler" <no-mail-please@nospam.com> wrote in message
|
Jon,
- The robot's loudspeaker will be in constant movement and so is the
microphone since it most likely will be a headset mic.
- Can't turn off speech recognition while the robot is talking. It is
designed such that most of the move it makes are accompanied by his voice.
Since I am using voice recognition to control his movements, and he talks
when he moves, I'm stuck with this environment (and so are all my users). |
|
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|
|
Robert Oschler
Guest
|
| Posted:
Thu Mar 31, 2005 7:01 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
| Quote: |
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
Lets take a different scenario. You have two microphones in a room and a
speaker who is not always in the same place. The microphones, although
the same model, are not identical; nor do they receive precisely the
same acoustic signal. What would need to happen in order for the output
of one of them to cancel the other's?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
|
Jerry,
What makes me think it will be easy? LOL. Apparently, as I stated at the
top of my message, my lack of expertise in DSP. :)
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
Thanks,
Robert |
|
| Back to top |
|
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Andrew Reilly
Guest
|
| Posted:
Thu Mar 31, 2005 7:47 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
On Wed, 30 Mar 2005 21:01:22 -0500, Robert Oschler wrote:
| Quote: | "Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
Lets take a different scenario. You have two microphones in a room and a
speaker who is not always in the same place. The microphones, although
the same model, are not identical; nor do they receive precisely the
same acoustic signal. What would need to happen in order for the output
of one of them to cancel the other's?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
Jerry,
What makes me think it will be easy? LOL. Apparently, as I stated at the
top of my message, my lack of expertise in DSP. :)
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
|
Oh, the art is pretty well known. It's the physics that makes application
of the art essentially impossible except under very tightly constrained
conditions.
To consider the two examples you gave:
Noise cancelling microphones are (a) generally bolted onto your head, so
that the relationship between their position and your mouth doesn't change
very much and (b) typically have a built-in second transducer in a known
(close) relationship to the first one. Speech is fairly limited in
bandwidth to start with, so reject everything outside that range. Then,
reject everything that has a propagation path inconsistent with the
direction of wave propagation from mouth past first and second microphones.
Noise cancelling headphones take advantage of the fact that they only have
to attempt to cancel sound waves in the tiny space between the speaker and
your eardrum. Even so, that means that they have no hope for signals
outside a certain frequency range thanks to the physical dimensions of the
problem, and rely to a fairly large extent on the (passive) blocking
capability of the headphone body.
Cheers,
--
Andrew |
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Andrew Reilly
Guest
|
| Posted:
Thu Mar 31, 2005 7:50 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
On Wed, 30 Mar 2005 20:56:18 -0500, Robert Oschler wrote:
| Quote: | - Can't turn off speech recognition while the robot is talking. It is
designed such that most of the move it makes are accompanied by his voice.
Since I am using voice recognition to control his movements, and he talks
when he moves, I'm stuck with this environment (and so are all my users).
|
Have you tried using a commercially available noise cancelling microphone?
I believe that they're pretty common for (say) car phone installations.
--
Andrew |
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|
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Robert Oschler
Guest
|
| Posted:
Thu Mar 31, 2005 8:05 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Andrew Reilly" <andrew-newspost@areilly.bpc-users.org> wrote in message
news:pan.2005.03.31.02.50.46.240286@areilly.bpc-users.org...
| Quote: |
Have you tried using a commercially available noise cancelling microphone?
I believe that they're pretty common for (say) car phone installations.
--
Andrew
|
Andrew,
I thought about it but most of the ones I saw were in the $70+ range. Since
my software is free, I'm trying to make entry into it as cheap as possible.
I'm finding out that only a handful of my users are willing to spend more
than around $15. If you know of anything, please let me know.
Thanks,
Robert |
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| Back to top |
|
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Andrew Reilly
Guest
|
| Posted:
Thu Mar 31, 2005 8:05 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
On Wed, 30 Mar 2005 23:27:19 -0500, Robert Oschler wrote:
| Quote: |
"Andrew Reilly" <andrew-newspost@areilly.bpc-users.org> wrote in message
news:pan.2005.03.31.02.50.46.240286@areilly.bpc-users.org...
Have you tried using a commercially available noise cancelling microphone?
I believe that they're pretty common for (say) car phone installations.
--
Andrew
Andrew,
I thought about it but most of the ones I saw were in the $70+ range. Since
my software is free, I'm trying to make entry into it as cheap as possible.
I'm finding out that only a handful of my users are willing to spend more
than around $15. If you know of anything, please let me know.
|
You almost certainly won't be able to do echo cancellation of the sort
that you're after with software on a PC: the minimum A/D +
buffer/compute + D/A latency is such that you can't even think about
generating an anti-signal in time for it to cancel the original, even if
you could nail down the movement and other physics-related problems.
You'll find that most echo cancellation systems (headphones, microphones)
of the sort that you've mentioned are analog, mainly for this reason.
It's possible to do echo cancellation in the digital domain (provided you
can make the physics nice) if you can make the acceptable lag from the
output, and the acoustic echo path length significantly longer than that
minimum processing latency. It's not clear from what you've described of
your system that this can be done, but I don't know for sure. Perhaps my
mental image of what you're trying to achieve isn't right...
Cheers,
--
Andrew |
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|
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Jerry Avins
Guest
|
| Posted:
Thu Mar 31, 2005 8:05 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
Robert Oschler wrote:
| Quote: | "Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
Lets take a different scenario. You have two microphones in a room and a
speaker who is not always in the same place. The microphones, although
the same model, are not identical; nor do they receive precisely the
same acoustic signal. What would need to happen in order for the output
of one of them to cancel the other's?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ
Jerry,
What makes me think it will be easy? LOL. Apparently, as I stated at the
top of my message, my lack of expertise in DSP. :)
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
Thanks,
Robert
|
The noise-canceling microphone is relatively simple. While not
completely effective, it does a pretty good job. It consists of two
microphones back to back, in essentially the same sound field as far as
distant sounds sources are concerned and so connected that their outputs
largely cancel. In use, the speaker talks directly into one side,
greatly unbalancing the sound pressures on the two elements.
Another way to look at a noise-canceling mike is as a microphone that is
relatively insensitive to common-mode (remote) signals but sensitive to
differential-mode (close-talking) signals. The salient difference
between it and what you propose is that its construction makes
cancellation at the source possible. No fixed reference such as the
sound that had been commanded can do that.
I wrote above, "Lets take a different scenario. You have two microphones
in a room and a speaker who is not always in the same place. The
microphones, although the same model, are not identical; nor do they
receive precisely the same acoustic signal. What would need to happen in
order for the output of one of them to cancel the other's?" The simple
answer is that the microphones need to be very closely matched and
located very near to one another. They need to respond to pressure,
which is (nearly) the same for both rather than to velocity, which
depends on the direction to the source and affects them differently.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Jon Harris
Guest
|
| Posted:
Fri Apr 01, 2005 1:34 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Robert Oschler" <no-mail-please@nospam.com> wrote in message
news:gtWdnRzZFt9wxdbfRVn-jQ@adelphia.com...
| Quote: |
"Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
|
As others have pointed out, those 2 examples are much different (and simpler)
than the problem you are trying to tackle, plus they are generally implemented
in (often analog) hardware, not software. |
|
| Back to top |
|
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Jon Harris
Guest
|
| Posted:
Fri Apr 01, 2005 1:38 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Jon Harris" <goldentully@hotmail.com> wrote in message
news:3b354nF6edbojU1@individual.net...
| Quote: | "Robert Oschler" <no-mail-please@nospam.com> wrote in message
news:gtWdnRzZFt9wxdbfRVn-jQ@adelphia.com...
"Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
As others have pointed out, those 2 examples are much different (and simpler)
than the problem you are trying to tackle, plus they are generally implemented
in (often analog) hardware, not software.
|
I should add, a better commercial example of what you want to do are the echo
canceling systems used commonly in teleconferencing. They solve the problem you
have, and do it in software (often with dedicated DSPs). However, even with
these, usually at least the loudspeakers are fixed and often the microphones are
fixed as well. But I would think a good fast-adapting echo canceller might be
able to give you at least some attenuation of the robot's voice. |
|
| Back to top |
|
|
Andrew Reilly
Guest
|
| Posted:
Fri Apr 01, 2005 6:04 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
On Thu, 31 Mar 2005 12:38:26 -0800, Jon Harris wrote:
| Quote: | "Jon Harris" <goldentully@hotmail.com> wrote in message
news:3b354nF6edbojU1@individual.net...
"Robert Oschler" <no-mail-please@nospam.com> wrote in message
news:gtWdnRzZFt9wxdbfRVn-jQ@adelphia.com...
"Jerry Avins" <jya@ieee.org> wrote in message
news:5r2dnSKXY6nKrdbfRVn-pw@rcn.net...
What makes you think it's easy? Imagine a robot swimmer in a pool. Since
you programmed it, you know its every move. In theory, you could
generate antiwaves that would create calm water wherever you want it. Of
course, you would need to account for reflection and diffraction from
the sides and objects in the pool.
After seeing so many noise cancelling microphones advertised, and headphones
like those that kill in-flight noise for airline passengers, If figured
wrongly that it had become a known art.
As others have pointed out, those 2 examples are much different (and simpler)
than the problem you are trying to tackle, plus they are generally implemented
in (often analog) hardware, not software.
I should add, a better commercial example of what you want to do are the echo
canceling systems used commonly in teleconferencing. They solve the problem you
have, and do it in software (often with dedicated DSPs). However, even with
these, usually at least the loudspeakers are fixed and often the microphones are
fixed as well. But I would think a good fast-adapting echo canceller might be
able to give you at least some attenuation of the robot's voice.
|
Actually, I really recommend that anyone who's interested just go ahead
and build one. It's a very simple exercise if you've got a microphone and
a DSP evaluation board of just about any sort.
You get a really cool "chirping" sort of sound as you move the microphone
through the sound field, and the echo response fails to line up with real
life. Quite captivating and musical, the time I tried it. (That was with
a simple, sample-at-a-time LMS update algorithm, rather than a faster,
block-update scheme. I suspect that a block-update adapter might work
better as a canceler, but not sound as nice.
By keeping the in-out delay low, and gating the impulse response
carefully, you can get some very odd effects, too. Like canceling the
body reverb. out of a piano or guitar recording. Plunk. Neat :-)
Cheers,
--
Andrew |
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| Back to top |
|
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Robert Oschler
Guest
|
| Posted:
Fri Apr 01, 2005 7:05 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
|
|
"Jon Harris" <goldentully@hotmail.com> wrote in message
news:3b35buF6dtkm0U1@individual.net...
| Quote: | "Jon Harris" <goldentully@hotmail.com> wrote in message
news:3b354nF6edbojU1@individual.net...
I should add, a better commercial example of what you want to do are the
echo
canceling systems used commonly in teleconferencing. They solve the
problem you
have, and do it in software (often with dedicated DSPs). However, even
with
these, usually at least the loudspeakers are fixed and often the
microphones are
fixed as well. But I would think a good fast-adapting echo canceller
might be
able to give you at least some attenuation of the robot's voice.
|
Jon,
Got any sources for any open source code I could try? I'm more than
willing to bang away at it. If not code, perhaps a really simplified
article with pseudo-code?
Thanks,
Robert |
|
| Back to top |
|
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Robert Oschler
Guest
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| Posted:
Fri Apr 01, 2005 7:09 am Post subject:
Re: Is there an Open Source Echo Cancellation module availab |
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"Andrew Reilly" <andrew-newspost@areilly.bpc-users.org> wrote in message
news:pan.2005.03.31.05.29.14.618874@areilly.bpc-users.org...
| Quote: | On Wed, 30 Mar 2005 23:27:19 -0500, Robert Oschler wrote:
"Andrew Reilly" <andrew-newspost@areilly.bpc-users.org> wrote in message
news:pan.2005.03.31.02.50.46.240286@areilly.bpc-users.org...
You almost certainly won't be able to do echo cancellation of the sort
that you're after with software on a PC: the minimum A/D +
buffer/compute + D/A latency is such that you can't even think about
generating an anti-signal in time for it to cancel the original, even if
you could nail down the movement and other physics-related problems.
You'll find that most echo cancellation systems (headphones, microphones)
of the sort that you've mentioned are analog, mainly for this reason.
It's possible to do echo cancellation in the digital domain (provided you
can make the physics nice) if you can make the acceptable lag from the
output, and the acoustic echo path length significantly longer than that
minimum processing latency. It's not clear from what you've described of
your system that this can be done, but I don't know for sure. Perhaps my
mental image of what you're trying to achieve isn't right...
Cheers,
--
Andrew
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Andrew,
I would think I have the computing resources to pull it off, but remember,
I'm a DSP ultra-novice. Although the signal is in real-time in that it is
the user talking into a microphone, the "listener" is a speech recogntion
engine not another person. I can therefore buffer as much audio signal as I
like for analysis purposes before sending it to the speech recognition
engine.
Obviously I'd like to keep it down to about 1/3 to 1/2 a second of
additional buffering. Otherwise the response time of the "speech to
recognized text" cycle will start feeling sluggish to the user.
Thanks,
Robert |
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