Re: Quality of CoreAudio SRC
Re: Quality of CoreAudio SRC
- Subject: Re: Quality of CoreAudio SRC
- From: William Stewart <email@hidden>
- Date: Mon, 4 Feb 2008 14:29:51 -0800
There were a couple of points that came up in this discussion that
I'll expand on
(1) Logic and SRC
As noted, Logic is using the CA SRC (though I'm not familiar enough
with Logic to know how settable for quality or algorithm that its uses
are). As with the use of the AUTimePitch in the Time Machine part of
Logic, our goal is not only to provide good, quality implementations
but also to provide a means by which 3rd parties can extend or
substitute particular features. So, for the usage of AUTimePitch
(which is an audio unit of both a "converter" and an "offline" type)
Logic has the ability to substitute other audio units to be used for
this functionality instead of AUTimePitch. This feature was added in
Logic due to a strong demand from Logic users and developers who
wanted this choice. So, if there is an interest here (to be able to
use other SRC's in Logic), please express that! (not here though, it
isn't really going to help much).
(2) iTunes and SRC
We have experimented with playback behaviour in some circumstances
where we change the playback sample rate to match the media sample
rate. We currently do this on iPhone and iPods. The real problem with
changing this is that it can introduce clicks and pops (sometimes
quite loud) in 3rd party output h/w. With our own analog outputs we go
to some length to supress clicks and pops (both on Desktops and
iPods), however, various USB devices and receivers (that can be at the
end of the digital outputs from desktop machines) unfortunately don't
always do this. So, the user experience can be quite bad, and we've
backed off from supporting this feature due to these unwanted side
effects. From the comments on the list however, I can clearly see that
this would be a desirable feature, so I'll advocate it again (maybe we
can have this as some kind of "advanced" or "expert" setting).
Thanks
Bill
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