Re: Record and playback at the same time
Re: Record and playback at the same time
- Subject: Re: Record and playback at the same time
- From: email@hidden
- Date: Fri, 13 Mar 2009 12:51:13 -0700 (PDT)
For VOIP, why would I have to consider the round-trip? If A is talking with B, A's microphone is picking up not just A's voice, but also B's voice, because B's voice is playing on A's speaker. So if I cancel B's voice, which I am playing on A's speaker, from the input of A's microphone, I should be fine, right?
----- Original Message ----
From: Hamish Allan <email@hidden>
To: Kyle Sluder <email@hidden>
Cc: email@hidden; email@hidden
Sent: Friday, March 13, 2009 12:30:28 PM
Subject: Re: Record and playback at the same time
On Fri, Mar 13, 2009 at 5:50 AM, Kyle Sluder <email@hidden> wrote:
> The typical way to do this is with a mix-minus. We do this in
> hardware at the radio station I work at; The output is split, and one
> of the outs is inverted and fed back in to the input. There is some
> gain and gating applied, and a miniscule natural delay due to the
> signal flowing through, so it works as intended.
I can see this working if the fidelity is high enough, but I'd have
thought that on the iPhone the speakers would distort the signal too
much for a mix-minus. Plus presumably your sound engineer tweaks the
gain, gating and delay until it's right, which you can't expect your
users to do. Also, if you're writing a VOIP application, you might as
well approach this as part of the harder problem, which is echo
cancellation from the round trip. Presumably Apple do this in
hardware, and as far as I can tell we don't get access to that
technology.
Hamish
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