Re: usb continuous output frequency format
Re: usb continuous output frequency format
- Subject: Re: usb continuous output frequency format
- From: Shaun Wexler <email@hidden>
- Date: Tue, 24 Dec 2002 12:55:09 -0800
On Tuesday, December 24, 2002, at 10:04 AM, Jeff Moore wrote:
The HAL provides the API for discovering and changing the stream
format of your device. The properties
kAudioDevicePropertyNominalSampleRate and
kAudioDevicePropertyAvailableNominalSampleRates are apropos here.
The fact that most apps just leave the device set to one sample rate
and do software rate conversion is pretty much common practice. There
isn't anything your device can do to force them to change the format
when they are happy with that arrangement.
On Monday, December 23, 2002, at 03:58 PM, Mark Ketilson wrote:
I have a USB device with an output channel that has continuous
frequency capability. It supports frequencies in a certain range and
returns that range. {4990, 55010} The device is set to 44.1 kHz as
the default.
The problem I'm having is that no audio program changes the frequency
of my device when I play files of a frequency other than 44.1kHz.
I'm wondering if there is a suggested method to add this
functionality to my device and why audio programs aren't able to
recognize the device capabilities.
What I see as the problem is that Mark's driver ONLY returns an
AudioValueRange of {4990, 55010} in reply to a
kAudioDevicePropertyAvailableNominalSampleRates call to the output
AudioDevice.
I suggest that the driver ALSO return ranges of {32000, 32000}, {44100,
44100}, and {48000, 48000}, so it matches the three supported "fixed"
input rates, as fixed rates are what most apps will be expecting.
In my app, I chose to build sample rate pop-ups with all the fixed
rates as individual items, and added one item for "Other..." when
encountering any variable ranges (coalesced), which when selected puts
up a sheet allowing direct text entry within of any of the variable
rate ranges.
--
Shaun Wexler
MacFOH
http://www.macfoh.com
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