[wdmaudiodev] Re: USBAudio sampling rate selection
- From: "carsten schulz (private)" <schulz.carsten@xxxxxxx>
- To: <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Mon, 19 May 2003 18:21:14 +0200
Hi Robert,
> Enumeration (Win98) is fine (except that CoolEdit Device=20
> Settings Dialog
> shows 11 kHz=20
> also supported (why?)=20
This is because KMixer is in the way and supports (with sample rate
conversion) more sample rates than your device provides. You should also =
see
other sample rates using CoolEdit (e.g. 44.1, 48) aren't you?
> but correctly refuses to record at this=20
> sample rate by
> showing=20
> MMSYSTEM008 Error).
I'm not sure, but this can be related to the fact, that CoolEdit only =
uses
WAVE_FORMAT_PCM (and not WAVE_FORMAT_EXTENSIBLE. I've seen problems on =
old
Win9x versions that had problems using WAVE_FORMAT_PCM on USBAUDIO =
devices.
What version of Win98 do you use? Win98 Gold, Win98 SE, with or without =
the
audio hotfix (QFE)? You should use Win98 SE at the very least. And I =
would
highly recommend to update to QFE 269601.
> But my Question is: How is the device told which sample rate=20
> to use?=20
There is no definite way to force Windows (i.e. KMixer) to use one =
specific
sample rate. KMixer depends on various assumptions when negotiating the
sample rate with USBAUDIO.SYS. It can be very tricky to find a scenario
under which KMixer always selects the wanted sample rate (i.e. the =
sample
rate that has been selected by the host application).=20
We solved this problem by providing an own filter driver that only =
supports
one sample rate at a time. The user selects the required sample rate =
from a
custom dialog and our filter driver hides
all the other sample rates from the USB descriptor.
Another way would be to restrict your customers to only use applications
that use the DirectKS API. As there are not too many applications out =
there
that uses this technology, I'm not sure if this would be appropriate for
your needs ;-)
Hope this helps.
Carsten
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