610 PDM Voice Activity Detector
610 : PDM Voice Activity Detector
- Author: Kevin
- Description: A one-tile spectral PDM voice activity score.
- GitHub repository
- Open in 3D viewer
- Clock: 1000000 Hz
How it works
This project is a compact activity-score estimator for a one-bit PDM microphone stream. It counts PDM ones over 64 clock cycles, measures how far that density is from the quiet midpoint of 32 ones, and accumulates 160 of those 64-bit windows into a roughly 10 ms frame at a 1.024 MHz PDM clock.
At the end of each frame, the circuit combines three tile-friendly features: low-weight frame magnitude, frame-to-frame magnitude change, and three square-wave mixer responses. The mixer phase steps are 8, 9, and 24 at the 16 kHz density-window rate, which approximate 500 Hz, 562.5 Hz, and 1.5 kHz spectral probes. These are not a full FFT; they are cheap signed accumulators that add a little frequency selectivity inside a single tile.
The internal score update is score = score - score / 64 + feature, with saturation at 255, and uo[7:0] reports that score once per frame. Quiet 50 percent-density PDM streams decay the activity toward zero, while speech-like energy changes and spectral responses drive it higher. The bidirectional pins are left unused and configured as inputs.
How to test
Apply a PDM clock, release reset, set ui[1] high, and present the PDM bit on ui[0]. Watch uo[7:0] for the smoothed activity score.
External hardware
None.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | pdm_data | score_bit0 | |
| 1 | sample_enable | score_bit1 | |
| 2 | score_bit2 | ||
| 3 | score_bit3 | ||
| 4 | score_bit4 | ||
| 5 | score_bit5 | ||
| 6 | score_bit6 | ||
| 7 | score_bit7 |