Is WASAPI limited to 44000Hz?

[Robert2]

Hi,
I am still running Audacity 2.0.4. I thought that WASAPI was limited to 44000Hz, but I just recorded streaming music through WASAPI with 96000Hz as the Project rate, and saved it to FLAC without any apparent problem.
Was the WASAPI limitation linked to the audio drivers (I just updated my Realtek drivers)?
Robert

[DVDdoug]

It gets rather complicated... I found some information on this page. It looks like there is a mode where Windows can re-sample whatever is coming out of the hardware. In another mode, you get whatever you hardware supports.

Was the WASAPI limitation linked to the audio drivers (I just updated my Realtek drivers)?

Yes. The drivers and the hardware. WASAPI is a driver protocol. From what I understand, there is a "driver stack" (where drivers talk to drivers, the digital audio stream passes through several drivers. Some of those drivers are supplied with Windows).

but I just recorded streaming music through WASAPI with 96000Hz...

Was that intentional? It's very unlikely that the streaming audio was 96kHz, so the main effect of up-sampling would be a bigger file.

[Robert2]

Hi Doug,
Information can be found on the following pages, but they are unclear what are the sample rate limitation of WASAPI.

WASAPI
About WASAPI
What's up with WASAPI?

Streaming audio can have high sample rates. Here is what is offered at http://www.sky.fm:

Our free service streams:

MP3: 96 kbits/sec
AAC-HE: 40 kbits/sec
Windows Media: 40 kbits/sec

Our Premium service streams:

MP3: 256 kbits/sec
AAC: 128 kbits/sec
AAC-HE: 64 and 40 kbits/sec
Windows Media: 128 and 64 kbits/sec

I normally use WDM-KS to record streaming audio or cassette deck output. It works fine on my system. I might be deluded but after extensive testing, I found that FLAC files created from WDM-KS recording at 96kHz gave me the best rendition (for classical music).

As I said, I have just updated my Realtek drivers to their latest Windows 8.1 version. So I checked that everything was still working fine. WDM-KS is still working fine. I also tested WASAPI out of sheer curiosity. Up to now I had assumed that WASAPI was limited to 48kHz (at some point, I read something to that effect in the Audacity online manual). But it turned out that I can (now?) use WASAPI to record at 96kHz, which is described as “Studio Quality” in the Windows Sound Panel applet. I could even use 192kHz which is supposed to be even higher “Studio Quality”.

Cheers,
Robert

[steve]

Streaming audio can have high sample rates. Here is what is offered at http://www.sky.fm:

I don't see anything there over 256 kbps even for the paid premium accounts.
"kbps" is not the same as "kHz".

"kbps" refers to then number of "bits" (a digital 1 or 0) per second (the "bit rate").

"kHz" refers to the sample rate. For CD quality, each sample period requires 4 bytes (2 bytes per channel) and a "byte" is 8 "bits". Thus for true CD quality (16 bits per channel, 2 channel stereo, 44100 samples per second) the "bit rate" is 1411200 bits per second, which is approximately 1400 kbps.

[Robert2]

You are right. There is interesting information on this subject at Check Bit Rate of Streaming Audio and What does the bit depth and sample rate refer to. Also audio samples at different bit rates are available from PowerStream Audio Samples and High Definition Audio Test Files.

It seems 160 kbps 44 kHz Stereo is the best we can expect from streaming audio.

[DVDdoug]

Just some reference points...

256 kbps (kilobits per second) is the (approximate) bit rate you get when you download an MP3 from Amazon or an AAC file from iTunes. (320kbps is the maximum allowed for MP3.)

44.1 kHz (samples per second) is the CD sample rate. DVDs are 48kHz. Recording studios typically record at 96kHz/24-bit.

For uncompressed audio, you can calculate the bitrate from the sample rate... CDs are stereo (2-channels) of 16-bit audio at 44,100 samples per second.

So... 44.1kHz x 2 channels x 16-bits = 1411.2 kbps for a CD.

And if you know there are 8 bits in a byte, you can calculate file size from the bitrate and the playing time.

...but they are unclear what are the sample rate limitation of WASAPI

As I understand it...

There are no limitations in the default mode. You can have a consumer soundcard/soundchip running at 48kHz and the drivers will hide that from you and make the conversion automatically to/from whatever you want. (That's what DirectX does.) Your printer basically does the same thing... You can send an image to your printer that's higher resolution than the printer can handle, and the printer driver automatically converts it to something the printer can handle.


In the exclusive mode you are locked-into whatever the hardware can do.

[Gale Andrews]

WDM-KS is still working fine.

The current 2.0.5 release of Audacity does not offer WDM-KS unfortunately because it causes Audacity to hang or the computer to crash on a few machines.

I also tested WASAPI out of sheer curiosity. Up to now I had assumed that WASAPI was limited to 48kHz (at some point, I read something to that effect in the Audacity online manual).

I don't think you did (or if you can find it, please point us to it so we can correct it).

The limitation is that the WASAPI loopback audio comes into Audacity at 44100 Hz (look bottom right of the Audacity window). Therefore if you choose other than 44100 Hz project rate, the recording will be resampled. It is better to avoid that. I don't think any of the developers knows for sure where that 44100 Hz limitation comes from. I don't believe shared or exclusive mode or the sample rate you choose in Windows "Sound" affects this.


Gale

[Robert2]

Hi Gale,
I meant the 44100 Hz limitation. This is why I prefer to use WDM-KS which I set at 96000Hz.

Now if I have 96000 Hz in the Windows Sound Applet, and 96000 Hz as the Audacity Default Rate, and I record using WASAPI, the “Actual Rate” in Audacity is also 96000 Hz (bottom right of the Audacity window). Does this mean that resampling from 44100 Hz to 96000 Hz is being done somewhere?
Robert

[Gale Andrews]

Now if I have 96000 Hz in the Windows Sound Applet, and 96000 Hz as the Audacity Default Rate, and I record using WASAPI, the “Actual Rate” in Audacity is also 96000 Hz (bottom right of the Audacity window). Does this mean that resampling from 44100 Hz to 96000 Hz is being done somewhere?

Assuming this is WASAPI loopback recording then the only relevant settings you can change in Windows are for the device that is playing the audio to be recorded.

Almost always, whatever rate I set the playback device's Default Format to in "Sound" (with the "Exclusive Mode" boxes checked or unchecked), the Audacity actual rate being recorded at shows 44100 Hz irrespective of Audacity Project Rate.

I have occasionally seen the recording "Actual Rate" be the same as "Default Format" (irrespective of the project rate) which is what I would have expected to happen (at least when Exclusive Mode is unchecked). But this seems a rare occurrence and most people always see 44100 Hz actual rate. If that happens and the project rate is some other rate then yes Audacity is resampling to the project rate. This often seems to cause poor recorded quality.

If you consistently see 96000 Hz actual rate when project rate is 96000 Hz, Default Format is 96000 Hz and Exclusive Mode is on, then there should not be any resampling anywhere.

What happens for you if you record with 48000 Hz project rate, Default Format 96000 Hz, Exclusive Mode on (both boxes checked)? You might think that actual rate would be 48000 Hz but I suspect what is meant to happen is that the actual rate is 96000 Hz. In any case (most of the time) I see actual rate of 44100 Hz in that scenario, and only very rarely 96000 Hz.


Gale

[Robert2]

I am running Windows 8.1, where things seem to be different from other (previous) Windows systems.

First, I don’t have two check boxes in the Advanced settings of the Windows Sound applet. I only have one check box for “Stereo Mix”, i.e. “Allow applications to take exclusive control of this device”.

Now, I consistently see 96000 Hz Actual Rate in Audacity when Project Rate is 96000 Hz, Default Format is 96000 Hz and Exclusive Mode is on.

However, the Audacity Actual Rate indicator is stuck at 96000 Hz, whichever Project Rate I choose. It seems the Audacity Actual Rate only shows the Default Windows rate. Or maybe the Audacity Default Sample Rate?

But there is more. If I record streaming audio from the Web in Audacity, and Exclusive Mode is on, I can play a completely different music through Foobar2000, and hear the two audio tracks playing together!

So it seems that Exclusive Mode is not working on my system.

Note that the same is true of Windows WDM-KS. Recording through WDM-KS in Audacity, and with Exclusive Mode on, I can hear two sound sources coming out of the speakers (that from Audacity and that from Foobar2000).

Windows works in mysterious ways!

Maybe this is due to the fact that I have no sound card, the audio and graphic chipsets are integrated into the main Intel G2020 chipset.

Robert