Re: Fwd: Odd issue with ALSA connecting directly to HDMI audio output

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Thank you, Takashi.

On Raspberry Pi 400 (one with built-in keyboard, although any RPi or Linux
computer with HDMI monitor with loudspeakers will do), open pd-l2ork (a
variant of pure-data available at http://bit.ly/pd-l2ork; pure-data also
has this same problem) and enable DSP. Do the same after changing audio
settings via the Preferences window (Edit->Preferences), where you can
switch among backends (ALSA vs Portaudio, vs JACK; JACK does not work with
any setting). If you have proper audio settings (0 in, 2 out, and a
supported SR, r.g. 44,1kHz), you will hear the buzz, and will also hear the
desired audio produced (e.g. by running Media->Audio Tester) faintly, with
buzz bring at the forefront. Or, you will hear everything OK (default Pulse
settings), or nothing. ALSA and PortAudio settings are default
Raspbian(RPi)/Ubuntu (desktop). Thank you.

Best,

Ico

-- 
Ivica Ico Bukvic, D.M.A.
Director, Creativity + Innovation
Institute for Creativity, Arts, and Technology

Virginia Tech
Creative Technologies in Music
School of Performing Arts – 0141
Blacksburg, VA 24061
(540) 231-6139
ico@xxxxxx

ci.icat.vt.edu
l2ork.icat.vt.edu
ico.bukvic.net

On Wed, Jul 19, 2023, 04:08 Takashi Iwai <tiwai@xxxxxxx> wrote:

> On Wed, 19 Jul 2023 07:58:17 +0200,
> Ico Bukvic wrote:
> >
> > Thank you for a follow-up. How would one set such a flag in alsa? Using
> > alsactl or by editing a config file? The app in question seeks to open
> the
> > audio hardware directly to minimize latency. Any examples are
> appreciated.
>
> Could you show how exactly you did test?
>
> The fact that PA works implies that the device is basically working
> when running with a proper setup (e.g. with hdmi:* PCM, etc.)
>
>
> Takashi
>
> >
> > Best,
> >
> > Ico
> >
> > --
> > Ivica Ico Bukvic, D.M.A.
> > Director, Creativity + Innovation
> > Director, Human-Centered Design iPhD
> > Institute for Creativity, Arts, and Technology
> >
> > Virginia Tech
> > Creative Technologies in Music
> > School of Performing Arts – 0141
> > Blacksburg, VA 24061
> > (540) 231-6139
> > ico@xxxxxx
> >
> > ci.icat.vt.edu
> > l2ork.icat.vt.edu
> > ico.bukvic.net
> >
> >
> >
> > On Tue, Jul 18, 2023 at 11:51 PM Geraldo Nascimento <
> > geraldogabriel@xxxxxxxxx> wrote:
> >
> > > On Tue, Jul 18, 2023 at 02:12:31PM -0300, Geraldo Nascimento wrote:
> > > > On Tue, Jul 18, 2023 at 12:22:35PM -0400, Ico Bukvic wrote:
> > > > > Hi all,
> > > >
> > > > Hi Ico and friends,
> > > >
> > > > >
> > > > > I have a consumer-level setup audio question. My research project
> uses
> > > a
> > > > > Raspberry Pi in conjunction with a small portable monitor that has
> > > built-in
> > > > > loudspeakers that are to be used via HDMI connection. The goal
> here is
> > > > > portability and minimal cost.
> > > > >
> > > > > Curiously, when trying to connect to monitor's loudspeakers (via
> HDMI)
> > > > > using ALSA, no matter what settings I pick, at worst I cannot get
> > > > > audio out, and at best, get a buzzy sound whose waveform is in the
> > > attached
> > > > > image. The sound is clearly periodic and impulse-like. It happens
> > > every 59
> > > > > samples. Changing sample rate increases pitch, suggesting 59
> samples
> > > remain
> > > > > constant regardless of the sampling rate. When playing the actual
> > > audio,
> > > > > you can hear it in the background, but this buzz is easily
> > > overpowering it.
> > > > >
> > > >
> > > > Ico, just a wild guess but are you sure you are not capturing the raw
> > > SPDIF
> > > > signal going through HDMI instead of Linear PCM audio signal?
> > >
> > > Here's a comment from the VC4 HDMI driver:
> > >
> > >  * HDMI audio is implemented entirely within the HDMI IP block.  A
> > >  * register in the HDMI encoder takes SPDIF frames from the DMA engine
> > >  * and transfers them over an internal MAI (multi-channel audio
> > >  * interconnect) bus to the encoder side for insertion into the video
> > >  * blank regions.
> > >
> > > And there's this perhaps closely related old issue with the vendor
> > > kernel and Android:
> > > https://github.com/raspberrypi/linux/issues/4654
> > >
> > > >
> > > > > Changing sample rate or bit depth, or buffering, makes no
> difference.
> > > > > Selecting 8 channels for output (one of HDMI's standards, as far
> as I
> > > can
> > > > > tell), sometimes manages to output a tiny chunk of a good audio
> > > sample, and
> > > > > then goes silent.
> > > > >
> > > > > Now, even more curiously, when using the portaudio backend and
> > > connecting
> > > > > to the default pulseaudio sink, works just fine. What could be
> causing
> > > this
> > > > > discrepancy?
> > > >
> > > > Perhaps PortAudio is forcing the Linear PCM bits on the underlying
> ALSA
> > > > backend somehow, see for example:
> > > > https://fossies.org/linux/alsa-lib/src/conf/pcm/iec958.conf
> > > > But this is just wild speculation, it may or may not be the case with
> > > > your report. It's best if you ask Takashi Iwai and Jaroslav Kysela
> > > > directly through the list with Cc: in case nobody else has any more
> > > > ideas of what could be the root cause of your report.
> > >
> > > You're probably sending PCM data to HDMI, which expects SPDIF frames
> > > instead, and PortAudio + PulseAudio seems to be aware of this. That's
> my
> > > theory at least. Setting the necessary bits and necessary IEC958 format
> > > on your ALSA playback may resolve your issue.
> > >
> > > >
> > > > Good luck,
> > > > Geraldo Nascimento
> > > >
> > > > >
> > > > > Best,
> > > > >
> > > > > Ico
> > > > >
> > > > > --
> > > > > Ivica Ico Bukvic, D.M.A.
> > > > > Director, Creativity + Innovation
> > > > > Director, Human-Centered Design iPhD
> > > > > Institute for Creativity, Arts, and Technology
> > > > >
> > > > > Virginia Tech
> > > > > Creative Technologies in Music
> > > > > School of Performing Arts – 0141
> > > > > Blacksburg, VA 24061
> > > > > (540) 231-6139
> > > > > ico@xxxxxx
> > > > >
> > > > > ci.icat.vt.edu
> > > > > l2ork.icat.vt.edu
> > > > > ico.bukvic.net
> > > >
> > > >
> > >
>




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