136 ADPCM Encoder Audio Compressor
136 : ADPCM Encoder Audio Compressor
- Author: Charlie Hess, Emil Ivanov
- Description: Accepts a microphone PDM input and returns an ADPCM encoded/compressed ouput
- GitHub repository
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- Clock: 0 Hz
How it works
This HDL block accepts a pulse density modulated (PDM) microphone signal and produces an encoded output at a lower sampling frequency while maintaining audio intelligibility.
Expected Inputs:
- clk (clk)
- slow_clk (ui_in[1]) for the ADPCM block at 1/8 frequency of clk
- Pulse Density Modulated input pdm_in (ui_in[2]) at clocked with clk
- block_enable (ui_in[3]) (active high): single bit enable for the entire block
Outputs:
- encPcm (uo_out[4:1]): the final 4 bit ADPCM encoded output
- outValid (uo_out[0]): Output Valid flag for the ADPCM block, goes high for one cycle of slow_clk each time a new valid adpcm value is output
How to test
Provide two synchronized external clocks, clk and slow_clk, slow_clk a frequency 8x slower than clk (e.g. clk = 512 kHz, slow_clk = 64 khz) Connect the data pin of a pdm microphone clocked with clk to pdm_in. Intially set block_enable to low, then when recording/compression should begin, set block_enable to high. Now, a CIC decimated and ADPCM encoded output of the microphone data will stream from encPcm, which can be stored to memory, or decoded for writing to an audio file or playback.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | clk | outValid | |
| 1 | slow_clk | ||
| 2 | block_enable | ||
| 3 | pdm_in | ||
| 4 | encPcm[0] | ||
| 5 | encPcm[1] | ||
| 6 | encPcm[2] | ||
| 7 | encPcm[3] |