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 > > > > > > > >
