Mobile Apps - 96KHz and 192KHz Sampling Frequencies

Asked By GSR

06-Nov-09 05:31 AM

Hi,

I am using Windows CE 6.0 R2.

I built a Windows CE Emulator PDA device in Debig Build.

When I used 96KHz / 192KHz audio .wav files they do not play properly.

Is there any limitation in Windows CE that it can support a range of
sampling frequencies only ?

Is it possible to give support of those sampling frequencies ?

Thank You & Regards,
GSR

07-Nov-09 02:55 PM

IIRC the emulator BSP I2S clock speed is hardcoded to 44.1kHz. The
emulator emulates an actual SMDK2410 eval board and while I beleave
the real SMDK2410 hardware is capable of 96 kHz, the emulator is not.

If you really need to do 96/192kHz audio tests, you are better off
doing those tests on real hardware with proper hardware support.

Henrik Viklund
Prevas AB

15-Nov-09 11:59 PM

Hi Henrik Viklund,

Thank You Very Much for your reply.

I have a OMAP Hardware which is interfaced with a TI's Hardware Audio Codec.
The TI's Hardware Audio Codec does supports 96KHz and 192KHz sampling rates.

The audio model being implemented is Wavedev2.

Either the wavedev2 mixer / Software Mixer which is running in waveapi.dll
can do Sample Rate Conversion, we are using a sample rate of 44.1KHz always
to the Hardware Auido Codec.

I have verified that, when the hardware audio codec is using 44.1KHz
sampling rate all the audio files (.wav format) whose sample rate is less
than or equal to 48KHz are played with out any issues.

When I tried 96KHz/192KHz raw audio files (.wav), they are not played
properly with the TI's hardware audio codec.

So, I thought of exercising the same thing on Device Emulator as it does
supports audio driver with wavedev2 implementation.

As of know I do not have any idea how to proceed in debugging with this issue.

Thank You & Regards,
GSR

16-Nov-09 03:50 AM

Hi,

Did you try to tune the Software Mixer to accommodate the hardware
sampling rate? (http://msdn.microsoft.com/en-us/library/ee483245.aspx)

For instance, to operate the Software Mixer at 96000 Hz, change the AC44
(44100) SampleRate value to 17700 (96000):

[HKEY_LOCAL_MACHINE\Audio\SoftwareMixer]

The Software Mixer is supposed to convert all inputs to the SampleRate
given in the Registry. It works well at least for rates up to 48000 Hz
(I checked it) but maybe does it have some difficulties to downsample
its input when the rates become 'high'?

In any case, one check I would do would be to calculate the rate at the
output of the Software Mixer, i.e. at the input of the driver write
routines. This should be feasible by counting the bytes and the time
elapsed between OPEN and STOP.

HTH
Remi


GSR a ?crit :

19-Nov-09 12:59 AM

Hello R. de Gravelaine,

Thank You Very Much for the reply.

As you suggested I changed the SampleRate registry entry for Software Mixer
to 8KHz (0x1F40). So, I have changed the Codec Sampling Frequency to 8KHz.

When I played a raw wav file with this configuration, it did not work, I can
see audio bar progresses on Windows Media Player. But, the Audio whatever I
hear is not clear. Which is not so when we used 44.1KHz sampling rate with
the Hardware Audio Codec and No entry for "SampleRate" in registry.

I am using a release build. I will try a Debug build, probably I will get
some Log from SW Mixer.

Still one concept was not clear. I understood that Wavedev2 can do Sample
Rate Conversion. If SW Mixer does Sample Rate Conversion based on
Convertes the audio input/output. Is it does on the same "SampleRate"
registry entry ?

The check whatever you suggested, that I have not tried. Once I complete that
I will update about that here.

Thank You & Regards,
GSR

19-Nov-09 04:29 AM

Hi,

There are a serie of articles that you should read if have not already,
at the Windows CE Multimedia Team Blog. For instance:

http://blogs.msdn.com/medmedia/archive/2007/01/12/what-do-you-mean-by-mixer.aspx
or
http://blogs.msdn.com/medmedia/archive/2007/01/03/windows-ce-audio-driver-samples.aspx
and in general most of the excellent articles by Andy Raffman:
http://blogs.msdn.com/medmedia/archive/tags/Author_3A00_+Andy+Raffman/default.aspx

I never used the wavedev2 model and never used sampling rates above
48000 Hz, but using either the MDD/PDD or the Unified Audio Model in
addition to the Software Mixer always gave me satisfaction, maybe
excepting on low-powered machines (the Software Mixer can consume a lot
of CPU power!)

I do not know either the way your hardware mixer works but I suspect some
kind of 'disharmony' problem between the soft and the hard mixers. You
know that a good sound can be produced at 44100 Hz 'everywhere' but that
8000 Hz does not work well. Did you try other classical rates such as
22050, 11025 and 48000 Hz?

To answer your question, I do not think that the SampleRate registry
should be used by someone else that the Software Mixer. Actually and
IMHO, using both software and hardware mixer is somehow overkill, as
they are supposed to roughly perform the same job. If I'd were you, I
would restrict to a single mixer in the chain to remove some unnecessary
complexity and CPU usage...

HTH
Remi


GSR a ?crit :

19-Nov-09 10:56 AM

OK, now you lost me... Can't say I have used the software mixer much in
CE (never above 48kHz) but are you saying you have audio hardware that
can do up to 192kHz/24bit but you use a software mixer to downsample
to 44.1kHz/16bit? Do you get no output whatsoever or is it distorted?
In the end, decent audio sample rate conversion is pretty resource-
consuming, especially when converting between rates that are not
multiples of eachother.

Henrik Viklund
Prevas AB

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22-Nov-09 04:25 AM

Hi,

Yes, I have an audio device which can support till 192 KHz and the output is
dostorted when I used a 192 KHz audio raw file, SW Mixer using a SamplingRate
of 44.1 KHz and HW Codec also using a SampleRate of 44.1 KHz (I2S Word Clock
= 44.1 KHz).

I understand what you are saying, in that case when we use a 8 KHz audio raw
file, it is also not a multiple of 44.1 KHz, but the audio output works just
fine.

I read the articles which are in the weblinks provided by the R. de
Gravelaine. Let me read them once again.

With no SampleRate registry entry (SW Mixer is running at a SampleRate of
44.1KHz), and when HW Codec is running with 44.1 KHz sampling frequency, I
have verified the following sampling frequencies 8KHz, 11.025KHz, 16KHz,
22.05KHz, 32KHz, 44.1KHz and 48KHz. I do not see any issues with playback and
recording for those frequencies. As soon as I use either 96KHz / 192KHz
sampling rates playback output is distorted.

Thank You & Regards,
GSR

23-Nov-09 04:32 AM

Hi,

Another outstanding thread is
http://groups.google.fr/group/microsoft.public.windowsce.platbuilder/browse_frm/thread/12ee87d5018dd784/8f086e5bc3145d69

This can give you indications on how to disable the Software Mixer.

HTH
Remi



GSR a ?crit :

26-Nov-09 08:25 AM

Hi R. de Gravelaine,

Thank You Very Much for your continuous help.

I noticed that in the current wavedev2 returns the below WAVEOUTEXTCAPS

case WODM_GETEXTDEVCAPS:
{
LPVOID pCaps = (PVOID)dwParam1;
DWORD dwSize = dwParam2;
static const WAVEOUTEXTCAPS wec =
{
0xFFFF,                        // max number
of hw-mixed streams
0xFFFF,                        // available HW
streams
0,                                  //
preferred sample rate for software mixer (0 indicates no preference)
6,                                  //
preferred buffer size for software mixer (0 indicates no preference)
0,                                  //
preferred number of buffers for software mixer (0 indicates no
preference)
8000,                             // minimum
sample rate for a hw-mixed stream
48000                            // maximum
sample rate for a hw-mixed stream
};

It looks no SW Mixer being used in our current wavedev2 driver. Only
differnece in those settings is, in the original post preferred sampling rate
set to 0. In our case preferred sampling rate set to 6.

Thank You & Regards,
GSR

26-Nov-09 10:05 AM

Hi,

OK. Let's assume the Software Mixer is disabled, although the '6' value
for *dwSwMixerBufferSize* (not dwSwMixerSampleRate!) does not look very
consistent!
In this case, the 48000 Hz value for dwMaxSampleRate does not look very
consistent either, if you want to be able to play 192000 Hz samples. Did
you fix this value?

Remi


GSR a ?crit :

18-Dec-09 02:10 AM

Hi,

I have to look at some other issues. That's why I could not reply for this
thread.

I have not modified the dwMaxSampleRate value, its set to 48000 Value.

However I have noticed that the Playback is working with 96KHz and 192KHz
sample rates when I used latest version of the BSP for OMAP35xx (My Hardware
is based on OMAP35xx). But, the recording fails for 96K / 192KHz sample rates.

I have not compared the older version of the Wave Driver and New Version of
the Wave Drivers yet.

My Apologies for late reply.

Thank You & Regards,
GSR