Re: 64bit processing possible?
Re: 64bit processing possible?
- Subject: Re: 64bit processing possible?
- From: Jeff Moore <email@hidden>
- Date: Thu, 30 Jul 2009 15:38:51 -0700
On Jul 30, 2009, at 3:21 PM, Brian Willoughby wrote:
On Jul 30, 2009, at 15:08, Jeff Moore wrote:
FWIW, the HAL and the driver model are the source of the usage of
32 bit floats as the canonical sample format, not AUHAL. So,
dropping down to the HAL doesn't really help you any. You will
still be using 32 bit floats to hold the data.
Thanks for the clarification. I was under the impression that you
have the option with the HAL of querying the hardware format (which
you surely can do) and then manually setting the data format to
match (which I could be wrong about).
Such things are possible, but all linear PCM formats are vended via 32
bit floats. Using 64 bit floats (provided you could find a bit of
hardware that supports it) would require jumping through the same
hoops as you need to to play encoded data.
Switching from AUHAL to HAL (besides adding a lot of headaches)
would remove any automatic AudioConverter later. But I guess
there's still the HAL mixer, which probably operates at 32-bit
float, between any host application and the raw audio driver.
This is correct. 64 bit floats would require the app to hog the device
and turn off mixing.
One caveat: the mixing happens in the driver, not the HAL. For kernel-
based devices, the IOAudioEngine does the work. For user-land devices,
it is in the hands of the driver as to where the mixing happens.
Does this explain why Digidesign are so hard-headed about removing
their audio interfaces from access by any other application whenever
Pro Tools is running? Are they do this to remove the 32-bit float
audio mixer from the processing chain?
I don't know.
On a similar note, is it possible to use 'hog' mode to force
CoreAudio to skip the 32-bit float mixing stage?
Yes, but the device has to support doing it. If it does, it would show
up as an available stream format for the device that has
kAudioFormatFlagIsNonMixable set. Note that you need to hog a device
before you will see the non-mixable stream formats.
--
Jeff Moore
Core Audio
Apple
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