USB audio type I IEEE_FLOAT descriptor

[AGhez]

Hi all,

I am using a STM32H7 and I implemented a composite usb device (CDC + AUDIO recording) using IAD interface descriptor.

I can successfully configure the audio interface as type I PCM (I tested both 16 and 32 bit), but if I try to configure the audio as type I IEEE_FLOAT windows does not recognize the microphone (the device is still present in device manager under 'sound devices', but there is no input device under 'Audio inputs and outputs'.

I just changed the wFormatTag field of the descriptor, leaving the bSubFrameSize=4 and bBitResolution=32.

Have I to change something else?

Thank you in advance,

regards

Arianna

[mohamed.ayed]

Hi , @AGhez​ 

I suggest to change the PID of device.

[AGhez]

Hi @mohamed.ayed​ ,

thank you for your reply, but I tried with no success!

Do you have any other suggestions?

thanks

[mohamed.ayed · Accepted solution]

Hi @AGhez​ 

It seems that windows USB audio 1.0 drivers does not support IEE_FLOAT

https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/usb-audio-class-system-driver--usbaudio-sys-

you need to switch to audio 2.0 class it is noted in microsoft documentation that audio 2.0 driver support IEE_FLOAT

https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers?source=recommendations

[AGhez]

Hi @mohamed.ayed​ ,

thank you for your reply! I read these articles but it wasn't so clear for me: "All Type I formats" for me means also IEEE_FLOAT, as it is reported in the USB AUDIO 1.0 specifications under the type I supported formats..

But since in the second article you linked the IEEE_FLOAT format is explicitly mentioned probably you are right.

Can you confirm me that there are not ST examples for USB AUDIO 2.0?

Thank you again,

regards

Arianna

[mohamed.ayed]

Hi @AGhez​ ,

actually ST USB lib support only audio class 1.0 but USBX (AzureRTTOS) middleware support both Audio 1.0 and audio 2.0 and we don't have an example audio 2.0 until now.

[Piranha]

> windows USB audio 1.0 drivers does not support IEE_FLOAT

The link you gave:

All Type I formats (except 8-bit signed PCM)

It took me a minute to find out...

https://www.usb.org/sites/default/files/frmts10.pdf

2.2.6 Supported Formats

The following paragraphs list all currently supported Type I Audio Data Formats.

2.2.6.3 IEEE_FLOAT Format

[AGhez]

Hi,

I got my device enumerated in USB Audio 2.0 (just enumerated, it is not really working), but I am experiencing the same issue: with format PCM the microphone appears between the recording devices, changing the format to FLOAT makes the microphone to not appear!

Any other clue?

Thank you,

regards

Arianna

[AScha.3]

why you insist on float ? this is very unusual for audio device, because standard is pcm or I2S in 16/24/32 bit (float not possible) ; these are the data formats, codecs use for audio in/out .

[AGhez]

I need 32 bit AND exclusive access: WASAPI does not support exclusive access with PCM 32 bits, but only with 8 and 16 bits, or with float, so that's why I am struggling with float..