Sock Master's Digi-512 Audio Digitizer

Screenshot of Digi-512

Digi-512 is an audio digitizer for the CoCo 3. It assumes you have 512K but lets you change the size of the playback/recording buffer so it can still be used on a 128K machine.

I was interested in audio digitizing on the CoCo, so I made up the program to experiment with a few different techniques or approaches at the process to see what method worked best to give the longest audio playback while still keeping good sound quality.
The CoCo has interesting hardware for Audio digitizing. Unlike other computers of the time, it actually has a built-in 6 bit DAC for audio playback. The CoCo's joystick port is also connected to the DAC and a comparitor so we can use the joystick port to digitize audio.

Digi-512 lets you choose between 3 different digitizing techniqes, and 4 different playback techniques:

  • Normal - Standard 6 bit audio digitizing and playback.
  • Enhanced - For playback only. It interpolates additional samples between known values to try to smooth out sound.
  • Compressed - Uses an extra 2 bits to store compression information in each stored byte. This allowed the digitizer to discard 0 to 3 'unnecessary' samples between each stored sample and increase recording time by an average of 150%.
  • 1-bit delta - To store only 1 bit of information for each sample. Effectively 8X storage compression, but it requires a high sample rate to sound good.

    • Audio Digitizer files

    Care should be taken to transfer the .DSK images to the correct disk sides using the correct number of tracks. Also note that Digi-512 does not automatically recognize the data format loaded, so you need to adjust the playback settings appropriately.
    digi-512.zip Digi-512 program disk. 35 track disk.
    1bitsim1.zip Sample music 1 - '1-bit delta - 62799 Hz' 40 track disk, side 1.
    1bitsim2.zip Sample music 1 - '1-bit delta - 62799 Hz' 40 track disk, side 2.
    compsim1.zip Sample music 2 - 'compressed - 12093 Hz' 40 track disk, side 1.
    compsim2.zip Sample music 2 - 'compressed - 12093 Hz' 40 track disk, side 2.
    mmmusic1.zip An experimental audio player & sample data part 1. 35 track disk 1, side 1.
    mmmusic2.zip sample data part 2. 35 track disk 1, side 2.
    mmmusic3.zip sample data part 3. 35 track disk 2, side 1.

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