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Sound_Effector

README.md

Turning the Nucelo board into a sound effector

This project is to implementation an effector with the following effects:

  • distortion
  • compressor
  • FIR filter (LPF, HPF and BPF)
  • Auto-pan and pseudo-stereo

12bit DAC has dynamic range of 20 * log10(2^12) = 72dB.

Pipeline

MEMS Mic -> DFSDM -> RAM/DMA -> CPU/DSP(effector) -> RAM/DMA -> DAC -> Analog filter (LPF + AC coupling) -> Headphone

DFSDM1 config

  • System clock: 80MHz
  • Clock divider: 52
  • FOSR: 32
  • Channel 2 right bit shift: 0
  • DMA peripheral-to-memory: circular

Resolution of PCM output at DFSDM

2 * 32^3 = 2^16 (16bit)

DAC1/TMR6 config

  • System clock: 80MHz
  • TMR6 counter period: 52 * 32 - 1
  • DAC1 trigger: TMR6 Trigger Out event
  • DMA memory-to-peripheral: circular

Synchronization between DFSDM1 DMA and DAC1 DMA

  • A master clock of both DFSDM1 and DAC1 is the system clock, so cyclic DMA at both DFSDM1 and DAC1 is synchronized with each other.
  • Start DFSDM1 DMA just after DAC1 DMA.
  • Use double buffer as follows:
DFSDM1 DMA            DAC1 DMA
[ A | B ] -- DSP --> [ A | B ]
  • DSP works on B while DAC1 is reading A, and vice versa.

Pins on Arduino connector

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  [ ]                                [*] PA5(DAC1 OUT2)
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  [*] GND                            [ ]
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  [ ]                                [ ]
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  [*] PA4(DAC1 OUT1)                 [ ]
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Enabling DAC1 OUT2 for stereo

Unfortunately DAC1 OUT2 is connected to PA5 pin that is also connected to the on-board LCD of Nucleo board. Cut the connection to the LCD by opening SB21: remove zero ohm chip registor from the Nucleo board.

Refer to the schematin on this web site: https://www.st.com/en/evaluation-tools/nucleo-l476rg.html

Analog filter

An analog filter is required to attenuate the DAC output voltage, to remove quantization noise and to remove DC offset from DAC output signal => Analog Filter