[wdmaudiodev] Re: Race to set record sampling rate on KMixer / KS pin / soundcard
- From: Waldemar Haszlakiewicz <waldemar.haszlakiewicz@xxxxxxxx>
- To: Evan Lerch <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Thu, 4 Mar 2010 16:30:54 +0100
I found another little thing in Win7... ControlPanel->Sound->choose Playback
device->Properties->Advanced leaf...
here you can select what kind of settings will specific channel have.
EL> Hi all,
EL>
EL> I am faced with a situation where my users must use two independent
software applications throughout the day: the
EL> first application (a phone) records audio at 8kHz and the second
application (an automatic transcriber) records
EL> audio at 16kHz. I am an engineer responsible for working on the
transcriber application.
EL>
EL> My problem is that if my users launch the phone first, Windows initializes
the sound system to a sampling rate of
EL> 8kHz. When the users subsequently launch the transcriber, the transcriber
requests 16kHz audio from the sound
EL> system. The sound system provides a 16kHz audio stream, but it is really
8kHz audio resampled by KMixer to 16kHz. This results in an unacceptable loss
of audio quality.
EL>
EL> I need to find a way to programmatically detect this situation. Upon
detection I would warn the user and provide
EL> problem resolution instructions. Something like "please launch transcriber
first, phone second."
EL>
EL> My question is: can you think of a way to programmatically detect this
situation? My first thought was to run FFT
EL> analysis on the recorded audio and look for relatively low amplitude in the
4kHz+ range. However, this approach
EL> isn't very deterministic, and the heuristics would be tricky to implement.
EL>
EL> What I'd really like is some way to query the Windows audio subsystem to
try and determine definitively what's
EL> going on. So I started learning about the Windows audio subsystems. I
gave up pretty quickly on waveIn, waveOut
EL> and DirectSound: they are too high level and don't know about what KMixer
and KS are doing behind the scenes. I
EL> looked into KMixer a bit, but it has no documented APIs.
EL>
EL> I then started looking into Kernel Streaming (KS), which has a huge API. I
started modifying the DirectKS example
EL> application to query filters and their pins for information. I tried many
approaches to querying the exposed KS
EL> filters and pins, with no luck. The KS APIs just seem like they aren't
designed to help an external observer query
EL> for detailed status information; they're more designed around a participant
in the system. For example retrieving
EL> certain pin properties requires a handle to the pin, and there is no way to
get a list of instantiated pin handles.
EL> The information that can be retrieved without pin handles seems unhelpful:
the format intersection information
EL> doesn't seem to change based on the pin's state. Some devices update their
pin's GLOBALCINSTANCES property, but
EL> others don't. KSPROPERTY_CONNECTION_DATAFORMAT seems like it can only be
set, not retrieved.
EL>
EL> I'm not very hopeful about finding an elegant solution to detecting this
situation. But, I've seen that there are
EL> a lot of knowledgeable people here and I thought it might be worth a query.
It seems like the problem might be
EL> relevant to others as well, since the problem can exhibit with any two
programs which want to record at different sampling rates.
EL>
EL> thanks!
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