Re: Native mode IO problems
Re: Native mode IO problems
- Subject: Re: Native mode IO problems
- From: Jeff Moore <email@hidden>
- Date: Tue, 2 Feb 2010 10:58:41 -0800
On Feb 2, 2010, at 9:37 AM, Stephen F. Booth wrote:
> I'm experiencing what I believe to be a buffer problem sending native
> format audio to an external DAC, but I haven't been able to figure out
> the cause.
>
> My goal is to send 24-bit ints directly to the DAC. I currently do
> something like the following:
> 1) Take hog mode
> 2) Grab the output AudioStream and set the physical format to
> non-mixable 24-bit PCM
> 3) Verify the virtual format changed to match the new physical format
> 4) Copy data in my IOProc (the data comes from a ring buffer populated
> in a separate thread)
Presuming that you have a step 1.5 in there that involves checking the stream's available format list to be sure that the device supports the non-mixable format you want, these procedures seem fine.
> I've tested this on a Benchmark DAC and on a Wavelength DAC. With the
> Wavelength DAC, everything comes out sounding as expected. However,
> with the Benchmark I hear repetitive glitching (approx. 2-3 times per
> second) that seems to indicate some sort of buffer problem.
>
> The strange thing is that if I send mixable floats to the DACs, the
> output is correct on both devices. It is only when I switch to
> non-mixable ints that I have the issue, and then only with the
> Benchmark.
>
> Does anyone have any ideas on what could be the cause?
I'm not familiar with these particular devices, but it sounds like the driver involved may not be co-operating with you on this. It may be that you are missing the step 1.5 above or it could be that the driver is advertising that it supports non-mixable formats when in fact it does not.
It's probably worth getting in touch with the manufacturer. Of course if the driver is an Apple driver (e.g. the USB Audio Class driver or the Firewire driver), you'll want to file a bug with us so we can take a look.
--
Jeff Moore
Core Audio
Apple
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