[Guide] Using Soxr Resampling with Rune 0.4 Beta

[janui]

[andfor]

[R101]

[janui]

Hi R101,
Your jlsounds dac uses an ak4490 chipset. This chip works only at 32bit. It seems that the alsa plug-in for the dac/chipset automatically forces this setting. It will be zero-filled if the source is lower, as you say it remains bit perfect.
janui

[R101]

Hi Janui,

The JLS "I2S over USB" is just an interface, not a DAC. To check that it should work, I have just tested it with Audacious + SOX plugin on a laptop running Lubuntu and counted 24 data bits per frame on an oscilloscope screen.

I do not know much about drivers. Does the Arch kernel have a different one from Debian?

MP3 streams are decoded to 24 bit and play OK, but I have never checked whether the actual output is 24 bit, or truncated.

[janui]

[R101]

Hi Janui, and thanks for your interest.

There is no problem with mpd itself, or the driver. I have checked, and 24 bit sources output a 32 bit word with 24 active data bits. Likewise, 16 bit sources output a 32 bit word with 16 active data bits.

I think there might be some confusion about word length and bit depth going on. Most DACs expect a 32 bit input per channel with the data either left-justified or I2S format, which means the driver does not care about bit depth, but needs to know the sample rate. The HAT drivers look like they use 24 bit words, though.

It seems in my case that Rune ignores what I am putting in the mpd.conf file. If I modify the file and go to the mpd settings in the Rune menu, I get a warning that the file has been modified and an invitation to manually modify it or reset it to default. Neither option seems to do anything.

All my efforts to find out more about SoX have come to nothing, as the documentation is aimed at those who already know what they are doing. I have tried removing the resampler section from the conf file and leaving the format line, as mpd is supposed to have a crude internal resampler, but this did not work either.

The SoX resampler works with the Audacious player via ALSA, so I think my problem must be something to do with the way Rune-mpd interacts with SoX, or perhaps another setting has disabled all software processing?

[janui]

[R101]

Janui,

You are still confusing word length with bit depth. They are not the same thing. The interface does not "force 32 bit", whatever that means. A 32 bit word is what it works with, whatever the bit depth or output format. Sample rate and bit depth are nothing to do with each other. If the format is set to "*:24:*" only the bit depth should be changed (if it does not match the original).

It does not matter what I put in the mpd.conf file, I have tried various options and all are ignored.

You do not seem to understand that a 320k stream does not in any way equate to sample rate. The BBC 320k feeds are 48k AAC encoded. I wonder if you have actually looked at the outputs you are getting from SoX, rather than what you think you are getting?