Fwd: Odd issue with ALSA connecting directly to HDMI audio output
Hi all,
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.
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?
Best,
Ico
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?
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.
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@vt.edu
ci.icat.vt.edu l2ork.icat.vt.edu ico.bukvic.net
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@vt.edu
ci.icat.vt.edu l2ork.icat.vt.edu ico.bukvic.net
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.
Best,
Ico
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@vt.edu
ci.icat.vt.edu l2ork.icat.vt.edu ico.bukvic.net
On Tue, Jul 18, 2023 at 11:51 PM Geraldo Nascimento < geraldogabriel@gmail.com> 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@vt.edu
ci.icat.vt.edu l2ork.icat.vt.edu ico.bukvic.net
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
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@vt.edu
ci.icat.vt.edu l2ork.icat.vt.edu ico.bukvic.net
On Wed, Jul 19, 2023, 04:08 Takashi Iwai tiwai@suse.de 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@vt.edu > > ci.icat.vt.edu > l2ork.icat.vt.edu > ico.bukvic.net > > > > On Tue, Jul 18, 2023 at 11:51 PM Geraldo Nascimento < > geraldogabriel@gmail.com> 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@vt.edu > > > > > > > > ci.icat.vt.edu > > > > l2ork.icat.vt.edu > > > > ico.bukvic.net > > > > > > > >
On Wed, Jul 19, 2023 at 02:39:44PM +0200, Takashi Iwai wrote:
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.
Hi Takashi, thanks for taking Ico's report. Perhaps the right configuration that he needs to use aplay could be: https://github.com/alsa-project/alsa-lib/blob/master/src/conf/cards/vc4-hdmi...
That is, if I understand correctly?
Thanks, Geraldo Nascimento
participants (3)
-
Geraldo Nascimento -
Ico Bukvic -
Takashi Iwai