On Wed, 19 Jul 2023 14:27:21 +0200, Ico Bukvic wrote: > > > 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. Well, the question is how the ALSA PCM device is opened, how configured and how played. As Geraldo already suggested, VC4 HDMI on RPi has a special format with IEC958 encoding. Also it has IEC958 status bit setups. So, for example, if you'd need to play a normal PCM stream with aplay, you'd need to open the device with "hdmi:$CARD" device -- then the rest is done in alsa-lib's plugin, and that's almost equivalent with what PA does. Takashi > > 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 > > > > > > > > > > > >
