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Forum Index : Microcontroller and PC projects : PicoMite audio

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Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 7820
Posted: 12:38pm 19 Jun 2025
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I understand that using the VOLUME command to reduce the sound level when using PWM audio reduces the bitrate and therefore the audio quality. However, is this true of the digital audio systems? I don't think it is, I think they are using either on-chip digital potentiometers or control within the DAC so this is no longer an issue. Can anyone confirm? Unfortunately my hearing isn't what it once was and I suspect that I couldn't hear a reduction in DAC bits until things got really bad!
Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 5023
Posted: 01:07pm 19 Jun 2025
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Hi Mick,

For PWM and DAC audio the bitrate remains the same (i.e. 44kHz) but you are correct that the audio at lower volume is only using part of it's dynamic range, so the signal looses granularity (quality degrades).

For I2S audio there are DAC's that have a built in gain stage (or " analog attenuator"). These will not suffer from this. But not all I2S chips have this attenuator.

You have to check the datasheet if the supported chips have an analog attenuator, or if they rely on digital attenuation (which has above loss of granularity). That being said... Most I2S DAC's are 16 but. And that it far better than the 12bit MCP4822 or 11.3 bit PWM audio. So you can sacrifice a few bits in the digital attenuation.

The I2S chips that have an analog gain stage built in control this gain stage in some way, either I2S, or I2C or SPI.

Regards,

Volhout
PicomiteVGA PETSCII ROBOTS
 
Mixtel90

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Joined: 05/10/2019
Location: United Kingdom
Posts: 7820
Posted: 01:41pm 19 Jun 2025
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Thanks Volhout. :)
Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs
 
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