Guru
Joined: 11/12/2012
Location: United KingdomPosts: 11636
| Posted: 05:59pm 06 Apr 2023 |
One limitation of uP is that the maximum PWM rate is limited by the CPU clock and the accuracy of the output as an analogue signal is then also limited
so in the case of the Pico 133MHz/44100 = 3015 steps = 11.5 bits of accuracy
However, there is a way of getting much more accuracy by combining two PWM signals for each audio channel
This is explained here
In this case with two channels you could have 16-bit accuracy with a much higher PWM frequency making filtering much easier or possibly unnecessary at all
Say 133MHz/(44100*11) = 274 steps. Now with two channels running together combined in a 256:1 ratio as in the document we get 16-bit accuracy with 11 PWM waves for each audio level at a PWM frequency of 44100*11 = 485KHz