Re: Quality of CoreAudio SRC
Re: Quality of CoreAudio SRC
- Subject: Re: Quality of CoreAudio SRC
- From: Jeff Moore <email@hidden>
- Date: Thu, 31 Jan 2008 15:01:51 -0800
Basically, what Stephen is saying is something we've been saying since
Day 0 of Core Audio and OS X. The hardware settings belong to the
user. They should not be changed by applications. Rather, applications
should be adapting to the settings of the hardware including
responding to dynamic state changes.
The basic reason why is that the audio system on OS X is designed to
be shared amongst all applications on the system. No application knows
enough to say with any certainty what is going in other applications.
Doing something like changing the sample rate can have serious
consequences to other applications on the system ranging from causing
a glitch in playback/capture or outright failure of some process due
to the interruption or temporary loss of synch. In a badly coded
application, it can cause a crash (see the recent thread about the bug
in HALLab for an example). In fact, I could go on about the bad things
that can happen to other applications when one app thinks it owns the
hardware and makes unwarranted changes to settings.
On Jan 31, 2008, at 2:30 PM, Mikael Hakman wrote:
On January 31, 2008 Stephen Davis wrote:
IMHO, it is bad form to be changing the audio hardware's sample rate
for each track. If you're gunning for the absolute highest quality
output then maybe it's okay but it's pretty obnoxious to the rest of
the system and should be clearly communicated to the user.
Would you or other knowledgeable member on this thread kindly
explain why rate-following would be bad, in absence of other rate-
locking signals such as digital input or word clock etc., please?
Why couldn't e.g. iTunes send the actual sample rate information
down the chain of software layers until it arrives to the hardware
(DAC)? The sample rate would need to be changed only when the rate
used by the actual track is different from previous. I have been
discussing this with few audio interface vendors. While they agree
that not doing SRC would be the best, they blame on application and
operating system vendors for not providing sample rate information
to their drivers/hardware.
For a user it is difficult if not impossible to keep track of what
sample rate a selected media is in, then use a control panel or
Preferences or both to change the rate, and first then to play the
track. Many users want to simply select a track, perhaps in Front
Row using a remote control from the couch, and play it, or even play
a number of randomly selected tracks. Why can't we give even these
users the best audio quality available on the system?
--
Jeff Moore
Core Audio
Apple
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