Re: Echo Cancellation on PC platform

It still seems strange that the soundcard, which is doing the
upsampling/downsampling in each case, would use a different rate for each. I'm
not familiar with the architecture of PC audio hardware, but it seems like it
would be harder to make it asynchronous then if playback and record used the
same clock. Is the 48kHz the exact same 48kHz for both playback and record?
Thanks for your info!

--
Jon Harris
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"Yehuda Mittelman" <liayehud@xxxxxxxxxxxxxxxx> wrote in message
news:dd22e7$ob$1@xxxxxxxxxxxxxxxxxxxxxxxxx
> The sound card can play/record only at a certain sample rate, usually it is
> 48khz. When you want to play a wav file at 8khz it has to internally upsample
> your 8khz data to 48khz in it's dsp and play it at 48khz.
> When you want to record at 8khz the sound card samples your microphone at
> 48khz and downsamples to 8khz.
> Some sound cards don't do it accuratly and that is why you have a mismatch.
>
>
>
> "Jon Harris" <jon99_harris7@xxxxxxxxxxx> wrote in message
> news:oQZIe.1406$2j.784@xxxxxxxxxxx
>> "Yehuda Mittelman" <liayehud@xxxxxxxxxxxxxxxx> wrote in message
>> news:dd05t8$cml$1@xxxxxxxxxxxxxxxxxxxxxxxxx
>>> You will have two problems:
>>>
>>> 2) some sound cards can only play the audio at 48khz. when such a soundcard
>>> has to
>>> play at 8000hz and record at 8000hz it's dsp uses a
>>> downsampling/upsampling
>>> algorithm.
>>> therefor you will see that you actually play the audio at 8000hz and
>>> record it at 8005hz or 8010hz or.... who knows...
>>> so you will have to detect that and convert your near_end or far_end
>>> samples
>>> accordingly.
>>
>> I've heard this before, but never really understood why this is the case. Can
>> you explain? Is the problem that the OS isn't locked to the sample rate on
>> the audio card?
>>
>
>


.

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