Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- Subject: Re: Does anyone get an AudioDevice that has both input and output channels? (question is related to software play through)
- From: Karl MacMillan <email@hidden>
- Date: Wed, 18 Jul 2001 18:53:30 -0400 (EDT)
On Wed, 18 Jul 2001, Jeff Moore wrote:
>
on 7/18/01 2:54 PM, Karl MacMillan <email@hidden> wrote:
>
>
> Playing from one device to another seems likely to fail to me if those two
>
> devices do not have a common clock source (which would be the case for
>
> most consumer cards). This is not an issue that can be solved by
>
> buffering because it is likely that this cards will run at different clock
>
> rates entirely (although they will be close) rather than just clock
>
> jitter. Do you guys have a solution to this?
>
>
Yeah, it's called Sample Rate Conversion based on incoming timing
>
information which is supplied in abundance by the Core Audio APIs. Audio
>
apps have been doing it for years. You can too. It's not that hard. I
>
suggest reading up on synchronization techniques in multi-rate systems in a
>
good DSP book.
>
I meant an integrated solution. Of course sample rate conversion is
possible.
>
> Also, I hate to see the introduction of this extra buffering - this api
>
> looks very promising in terms of latency (and the output only tests I have
>
> done seem to work well) but unless 1 IOProc can deliver both input and
>
> output I think this will always fall behind something like ASIO.
>
>
ASIO can't magically unify two physically separate devices either.
>
No, but it does provide one callback for a single device.
>
> So again, will the built-in audio device driver be fixed?
>
>
I say to you again, that if you really are going to do this, then it doesn't
>
matter since most devices don't support it anyway. You need the general
>
technique or you will not have this feature in your app for most audio
>
devices because you are not willing to do the extra work or buffer up a bit.
>
It is not a matter of 'extra work' but rather of efficiency. The
buffering will have a very negative effect on latency. Of course a
general solution is required, but for the common case (a single sound
card) it would be nice if one callback could be provided.
Previous posts on this lists suggested that this functionality would be
provided. I am simply wondering if this has changed.
Finally, I assume by the sarcastic tone of your reply that I have offended
you in some way. This was not my intention and I apoligize if I have done
so.
Karl
>
--
>
>
Jeff Moore
>
Core Audio
>
Apple
>
_______________________________________________
>
coreaudio-api mailing list
>
email@hidden
>
http://www.lists.apple.com/mailman/listinfo/coreaudio-api
>
_____________________________________________________
| Karl W. MacMillan |
| Computer Music Department |
| Peabody Institute of the Johns Hopkins University |
| email@hidden |
| mambo.peabody.jhu.edu/~karlmac |
-----------------------------------------------------