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About this repository

This repository contains the software part of my diy-audio project that features an XMOS xCORE-200 embedded processor. For the associated hardware project, please refer to https://github.com/sa9ra1xken/hw_xSSDAC.

USB DAC and SD audio player application

"Module app_usb_sdc_ssdac_xSSDAC-SD-V2" included in this repository is an implementation of a USB DAC and SD card audio player function that runs on the Hardware.

Feature

USB audio and SD audio player functions can be selectable on the menu screen.

  • USB Audio supports incoming stream up to 24bit stereo @ 384Ksps (depending on interpolation mode).
  • SD audio player supports linear PCM AVI and Flac format files up to 24bit stereo @ 192Ksps (depending on interpolation mode)

Interpolation and DAC control

In this implementation, the interpolation process corresponding to so-called oversampling is not performed by hardware but by software. Instead of conventional FIR-filter-based interpolation, this implementation uses cubic spline interpolation that was introduced as SSDAC in "トランジスタ技術" magazine, issue of October 2018.

Not only cubic spline interpolation, but the below types of interpolation modes are selectable by the menu screen.

  • SSDAC (Cubic spline interpolation), the maximum supersampling factor of 32 depending on the source sample rate.
  • NOS (no oversampling)
  • linear approximation
  • SINC-function-based FIR filter for oversampling factor of 4
  • SINC-function-based FIR filter for oversampling factor of 8

Operation Console

Consists of a four-line character display and 7 push button switches.

OLED_and_7_buttons

The state of the console consists of the following 3 modes. The console mode changes by pressing SW7.

graph LR;
state1(Track control mode);
state2(Interpolation selection mode);
state3(function selection mode);
state1 --> state2;
state2 --> state3;
state3 --> state1;
Loading

In track control mode

Button SW1 SW2 SW3 SW4 SW6 SW5 SW7
Click Previous track rewind 10 sec Stop/Start foreward 10sec Next track Console mode
Hold down Previous folder Next folder

In Interpolation selection mode

Button SW1 SW2 SW3 SW4 SW6 SW5 SW7
Click SSDAC Step (NOS) Linear FIR x 4 FIR x 8 Console mode

In Function selection mode

Button SW1 SW2 SW3 SW4 SW6 SW5 SW7
Click USB DAC SD player

The selected function takes effect on the next boot (reset button).

Development environment

xTIMEcomposer 14.4.1. later versions may be ok though Auther has not tried.