ProtoDAC TDA1387 X8 project

[smokey_mountain]

Folks,
Finished building ProtoDAC and RaspberryPi arrived, installed MoOde. I have mix of 16, 24 and DSD music files thus on the question of Camilla-based Dithering...

@Tim Curtis has kindly explained in his write that Camilla can be used for 1) Polarity Inversion (together with Flat Dither to 16) OR 2) Resampling.

I would like to use Resampling config steps (taken from Tim's instructions copied below).

Question: if I use Camilla Resampling do I need to use ALSA Polarity Inversion or Camilla Resampling Config also gives Polarity Inversion?

Thanks in advance!

5.2 Polarity Inversion
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The ProtoDAC output polarity is inverted and thus a Polarity Inversion operation must be performed on the input signal so that correct +/- polarity is output to the loudspeakers.
Two polarity inversion options are included in moOde. The first is ALSA based which is available in the Music Player Daemon (MPD) section of the Audio Configuration screen. The second is CamillaDSP based which is available in the CamillaDSP Configuration screen.

ALSA Polarity Inversion

• Menu, configure Audio
  
• Scroll down to the "MPD Options" section
  
• Scroll down to "DSP options"
  
• Turn "Polarity inversion" on
  

CamillaDSP Polarity Inversion

This assumes at least CamillaDSP version 2.0.1 and the sample configs have been updated to version 2. The "V2-ProtoDAC" configuration used here has the following description:

Code:

ProtoDAC TDA1387 X8 Non-oversampling DAC. Invert +/- signal polarity on both channels and apply Flat dither to 16 bit samples.

• Menu, Configure, CamillaDSP
  
• Turn "Default device" on
  
• Set "Signal processing" to V2-ProtoDAC
  
• Click SAVE
  

5.3 Resampling

Playback at the native bitrate of the source audio is recommended but sometimes if specific types of distortion are audible, resampling to a higher bitrate can be used to help reduce this distortion.
One type of distortion that may be reduced by resampling is Intermodulation (IM) distortion. IM distortion is caused by the presence of ultrasonic sample images. Resampling to 384 kHz will push these ultrasonic images past 192 kHz at which IM distortion would likely be inaudible.
Another type of distortion that may be reduced by resampling is band-edge response droop which is commonly referred to as "sinc droop". This typically occurs at 20 kHz but may also occur with greatly reduced effect in lower bands.
The ProtoDAC supports sample rates from 44.1 kHz to 384 kHz and accepts bit-depths from 16 to 32 bits where the Least Significant Bits (LSB) over 16 are ignored.
Two resampling options are included in moOde. The first is Sound eXchange (SoX) based which is available in the MPD Configuration screen. The second is CamillaDSP based which is available in the CamillaDSP Pipeline Editor screen.
SoX Resampling

• Menu, Configure, MPD
  
• Set Enable to "Yes"
  
• Set Bit depth to "Any" or optionally to "16" if you want SoX to manage bit depth conversion instead of ProtoDAC. In this case set "Default device" to OFF in CamillaDSP Config otherwise the bit depth will default to the highest bit depth reported by ProtoDAC which is 24-bit.
  
• Set Sample rate to the desired rate up to 384 kHz
  
• Leave Channels set to "Stereo"
  
• Leave Quality set to "High (Default)"
  
• Click SAVE
  

CamillaDSP Resampling
[url=https://github.com/moode-player/protodac/blob/main/docs/protodac_tda1387_x8.md#camilladsp-resampling]

• Menu, Configure, CamillaDSP
  
• Set Signal processing to "V2-ProtoDAC"
  
• SAVE
  
• Scroll down to the Pipeline editor section
  
• Set Status to "ON"
  
• Set Expert mode to "ON"
  
• Click OPEN
  
• Click the Devices tab
  
• Set samplerate to the desired rate
  
• Set resampler_type to "AsyncSinc"
  
• Set profile to "Balanced"
  
• Set capture_samplerate" to "Default"
  
• Set Playback Bit depth to to "16" if you want CamillaDSP to manage bit depth conversion instead of ProtoDAC. In this case set "Default device" to OFF in CamillaDSP Config otherwise the bit depth will default to the highest bit depth reported by ProtoDAC which is 24-bit.
  
• Click "Apply and save" to save the settings to the configuration file