6Bit audio:

Using, learning, programming and modding the Gigatron and anything related.
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axelb
Posts: 41
Joined: 07 Jan 2021, 06:27

Re: 6Bit audio:

Post by axelb »

In order to test our 8 bit DAC I played a bit with at67’s miditones / gtmidi / gtbasic toolchain.
The following sample was recorded from the output of the audio module by means of Audacity for Windows
audio 6 bit.mp3
(346.79 KiB) Downloaded 179 times
This is the standard output of the Gigatron for comparison:
audio 4 bit.mp3
(367.26 KiB) Downloaded 157 times
at67
Site Admin
Posts: 647
Joined: 14 May 2018, 08:29

Re: 6Bit audio:

Post by at67 »

Awesome, the difference in quantisation noise is clearly audible, it sounds like you're using Sine waves as the channel samples?
lb3361
Posts: 360
Joined: 17 Feb 2021, 23:07

Re: 6Bit audio:

Post by lb3361 »

Sounds pretty convincing.

Is there a way to say how much is related to the additional bits, and how much to the better analog circuitry?

That said, my understanding is that Marcel's code treats each channel as 6 bits (saturating at 63). Adding four channels yield 8 bits before truncating the low 4 bits. Therefore, if one only uses one channel, only 2 bits are really used. At67's demos seem smarter than that though...
axelb
Posts: 41
Joined: 07 Jan 2021, 06:27

Re: 6Bit audio:

Post by axelb »

I used a sine wave in waveform 2 as in your Music64k example !

The main improvement in respect to sound quality is certainly due to the better resolution of the DAC. An audible difference between 6 and 8 bit may depend on the sound sample preparation, though.
In addition low-pass filtering on the audio board very effectively suppresses high pitch noise. This makes the sound more pleasant - especially when directly connecting headphones to the board.
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