Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
- Subject: Re: Two AUHALs, one ring buffer, and one AU filter. But no sound.
- From: Jeff Moore <email@hidden>
- Date: Wed, 7 Jul 2004 11:45:16 -0700
On Jul 7, 2004, at 3:50 AM, Sven Behne wrote:
Am 01.07.2004 um 16:45 schrieb William Stewart:
This is why you use the varispeed between the input and the output
side.
The varispeed's rate is set as the relationship between the rate
scalar
of the input and output devices...
We're preparing some sample code that does this
Bill
Bill,
is the varispeed you're writing about the "mRateScalar" member of the
AudioTimeStamp?
Specifically, you have to resample the data from the slave devices to
match the rate scalar of the master device.
And if that should be the case:
- Is mRateScalar = nomimal sample rate / actual sample rate?
The rate scalar that the HAL vends is the ratio between the observed
number of host clock ticks per sample and the nominal number of host
clock ticks per sample.
- If you start an AudioDevice, how long does it take until mRateScalar
is "stable"?
It depends on the hardware involved. Most are stable within some small
number of laps around the ring buffer. Some less. Some more. Usually,
FireWire and PCI hardware stabilize the fastest as they have the finest
grained clocks.
Also, don't forget that this is a dynamic thing. The amount of clock
drift can and does change as a function of time, especially if an
external synch source is involved.
--
Jeff Moore
Core Audio
Apple
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