About the length of I2S output of PI3...

andre_chang

Hi
I found that the 44.1K 48K DATA data length is 16 bits. Can it be restored to the standard 32 bit length (plus 16 empty bits)?

Thank you
Andre

janui

Hi andre_chang,

Yes. But not quite sure what you are trying to do.

Tell us: the type of Pi and image you are using, your DAC/audio card model and what you want to do.

Posting your debug also helps us to answer your questions.

janui

hondagx35

Hi andre_chang,

Can it be restored to the standard 32 bit length

What standard you are talking about?

If your DAC needs a 32bit datastream MPD and ALSA will do bit stuffing (filling with zeros) on the fly for you.

Frank

andre_chang

hi janui & frank:

Question 1:
I want to make a Pi2 or PI3 I2S adapter to output SPDIF signals. But...

After installing the rune system on pi2, I found out that when Rune played a 16 bit file, the length of the data frame was only 16 bits, and when it played 24 bits, it was 32 bits.
But on a volumio or moode system, the data length is 32bit...

Because SPDIF synthesis chip (such as WM8805) only supports 32bit data length.

When Rune plays 16bit music, can the length of data BCK data of I2S output 32bit?

How can I set the length of Rune if 32bit can be output?

Question two:
Can the run output SRC lock 44.1 Khz, or can the SPDIF always output 44.1 kHz regardless of the playback rate of 44.1 kHz to 384 khz?
If so, what should I do?

Rune beautiful voice surpasses other systems! I like it!

Andre

Attachments

: 16bit.jpg (61.88 KiB) Viewed 2789 times

: 24bit.jpg (64.09 KiB) Viewed 2789 times

: pi2.jpg (112.92 KiB) Viewed 2789 times

R101

andre_chang,

I think the slot length will be decided by the driver. You might find it easier to use a USB to s/pdif interface, or a s/pdif HAT with its own driver.

janui

Hi andre_chang,

I think you first need to experiment with a few settings in order to determine how you want to set this up. After deciding on the set-up, we can help you automate setting these values.

1. 24le (24 bit little endian) is always (at least on the Pi with MPD) encoded as zero filled 32le.
2. For reference see this document: https://www.musicpd.org/doc/html/user.html#chapter-3-configuration
3. To make all output from MPD 32 bit (zero filled if required) you need to modify the relevant audio_output block of /etc/mpd.conf. The audio_output block looks something like this:

audio_output {
    type "alsa"
    name "my ALSA device"
    device "hw:0"
}

You need to add a format clause 'format "*:32:*"', this means: "any bitrate : always 32 bit : any number of channels". The modified audio_output block will look something like this:

audio_output {
    type "alsa"
    name "my ALSA device"
    device "hw:0"
    format "*:32:*"
}

4. To additionally make all output from MPD 44.1Khz again the fomat clause is used, this time with a value of 'format "44100:32:*"', this means: "always 44100hz : always 32 bit : any number of channels". The modified audio_output block will look something like this:

audio_output {
    type "alsa"
    name "my ALSA device"
    device "hw:0"
    format "44100:32:*"
}

If the audio source is not 44.1Khz MPD will automatically carry out resampling, this will always reduce your sound quality. Using SoXr as resampler plugin gives reasonable results, much better than the built-in MPD resampler. Look at the documentation and listen to the results. This may not give you the quality which you expect.

To automatically set these parameters in Rune we will need to know the type of audio card which you are (or will be) using. Let us know what this is.

janui

andre_chang

Hi janui:

We can set up HiFiBerry DAC in CONFIG.TXT.
The conversion chip will use WM8805 to output SPDIF signal ~

Do you have steps to install SOXr plug-ins and enable them?

Thank you!

andre

janui

Hello andre_chang,

MPD needs to be built with the SoXr option to be able to use it. Look at the results of:

mpd --version

It is included if you see this, or something similar:

...
Filters:
 libsamplerate soxr
...

You should look for the word ‘soxr’, it may be in a different section depending upon the version which you are using. If it is not there MPD will need to be upgraded. I have a couple of pre-built versions which you may be able to use, please tell me the version number which you are currently using.
Swtching SoXr on is dependant on the version of MPD. For v0.19.xx the following line needs to be included in /etc/mpd.conf :

samplerate_converter “soxr very high”

For v0.20.xx this needs to be added to /etc/mpd.conf :

resampler {
  plugin "soxr"
  quality "very high"
}

MPD will fail to start if you set Soxr ON when it is not built in.

See the following post for modifying the file /srv/http/db/redis_acards_details file. This is a way of automatically adding the ‘format’ output_block clause for the Hifiberry DAC: #4434455

We need Franks help to do the same for your WM8805.

janui

andre_chang

hi janui:

Attachments

: ALSA.jpg (154.58 KiB) Viewed 2740 times

janui

Hi andre_chang,

For your I2S testing I suggest that you use the hifiberry dac overlay.

Run these commands to automatically add the 'format "*:32:*"' clause to the audio_output block for the hifiberry dac:

sed -i -e '/snd_rpi_hifiberry_dac/s/)","hwplatformid":/)","card_option":"format\\t\\"*:32:*\\"","hwplatformid":/' /srv/http/db/redis_acards_details
redis-cli del acards
php /srv/http/db/redis_acards_details

Then select the hifiberry dac overlay (this depends on the image which you are using: via the Settings IU or by editing /boot/config.txt) and then reboot.

You will then see that /etc/mpd.conf contains the format clause. To activate it, you will need to select the audio output via the MPD UI.

janui

PS look here for an explanation of what the sed command is doing: #4434455

andre_chang

Hi janui:

You are wonderful!!

My Rune has been able to output the required length correctly.

For the problem that the output of Rune spidf is always 44.1KHz, I do not see soxr.. On MPD.
Please teach me how to install this plugin, thank you again.

Once again, you are wonderful!

janui

Hi andre_chang,
To set up SoXr see your PM.
To set up 44.1Khz you need to edit /srv/http/db/redis_acards_details, look for the line containing both 'snd_rpi_hifiberry_dac' and '*:32:*'. In this line change '*:32:*' to '44100:32:*'. Then run :

redis-cli del acards
php /srv/http/db/redis_acards_details

Then reboot.
You could change it to '*:*:*' to switch off the modification completely. Look at my previous post in this thread which explains how the format clause works.
janui

andre_chang

janui wroteHi andre_chang,
To set up SoXr see your PM.
To set up 44.1Khz you need to edit /srv/http/db/redis_acards_details, look for the line containing both 'snd_rpi_hifiberry_dac' and '*:32:*'. In this line change '*:32:*' to '44100:32:*'. Then run :
redis-cli del acards
php /srv/http/db/redis_acards_details
Then reboot.
You could change it to '*:*:*' to switch off the modification completely. Look at my previous post in this thread which explains how the format clause works.
janui

hi janui:
My MPD doesn't seem to have SoxR plugin.

Attachments

: soxr.png (17.47 KiB) Viewed 1788 times

janui

Hi andre_chang,
Yes, please log in to the forum and look at your messages.
janui