Raspberry PI 2B/3 and USB audio

[Herbert J. Skuhra]

On Mon, 12 Nov 2018 20:46:13 +0100, "Herbert J. Skuhra" wrote:
> 
> On Sun, 11 Nov 2018 13:52:14 +0100, Hans Petter Selasky wrote:
> > 
> > On 11/10/18 12:24 PM, Herbert J. Skuhra wrote:
> > > Hi,
> > > 
> > > if you use an USB sound card on your Raspberry PI 2B/3, can you please
> > > answer the following questions:
> > > 
> > > - which USB sound card?
> > > - do you have bad audio on current or stable/12 after r339388?
> > > 
> > > My "Creative Technology Ltd Sound Blaster Play 2" device sounds very
> > > bad. Meanwhile more changes were commited but they don't fix audio
> > > completly.
> > > 
> > 
> > Hi,
> > 
> > Some background:
> > 
> > The USB controller in Raspberry PI is running HIGH-speed USB. Many USB
> > audio device are FULL-speed USB. In order for a FULL-speed USB device
> > to work in a HIGH-speed USB environment all data transfers need to go
> > through a so-called transaction translator. This transaction
> > translator operate on chunks of data, 171 bytes maximum. That means if
> > a USB audio stream generates 1000 packets per second, then suddenly a
> > bunch of smaller packets will be needed. This puts some stress on the
> > DWC OTG driver and there might be some room for improvement in this
> > area too, but the basic sympthom is that the DWC OTG driver in FreeBSD
> > is not always able to keep up with the timing required for these
> > so-called split transactions. One idea is to move all DWC OTG IRQ
> > handling away from CPU-0. I'm not sure if cpuset supports this yet on
> > armv7 // arm64. Might have to be done in the driver.
> > 
> > Further some audio device use non-adaptive clocks, which means the
> > recording channel must be active along with the playback channel else
> > jitter will occur.
> > 
> > The recommendation for RPI is a HIGH-speed USB audio device (should be
> > clearly marked in the specification). Using a HIGH-speed USB audio
> > device will reduce the number of interrupts significantly.
> 
> Well, the sound card worked perfectly fine so far... both on FreeBSD
> and Arch Linux ARM... no luck with NetBSD. Never mind! I am obviously
> the only user affected by this "fix" (r339388).

Unfortunally I've purchased another full-speed usb audio device:

uaudio0 on uhub1
uaudio0: <Creative Technology Ltd Sound Blaster Play 3, class 0/0, rev 2.00/1.06, addr 4> on usbus0
uaudio0: Play: 96000 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: Play: 88200 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: Play: 48000 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: Play: 44100 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: Record: 48000 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: Record: 44100 Hz, 2 ch, 24-bit S-LE PCM format, 2x8ms buffer.
uaudio0: No MIDI sequencer.
pcm0: <USB audio> on uaudio0
uaudio0: HID volume keys found.

While it works fine under Linux (pulse), MacOS and Windows, it
produces only bad noise under FreeBSD (Raspberry PI3B)! :-(

How can I get it working? Can anyone recommend an USB audio device for
FreeBSD? Should DACs from Pro-Ject work?

Thanks.

--
Herbert