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add bandpass filter for PDM mics

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This introduces an optional band pass filtering step to remove low frequency noise. Very effective for PDM mics - reduces noise floor by a factor of 100 !
This commit is contained in:
Frank
2022-11-17 15:09:54 +01:00
parent eb2bf421b0
commit d3af3446f7
2 changed files with 68 additions and 8 deletions
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4
usermods/audioreactive/audio_source.h
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@@ -220,7 +220,7 @@ class I2SSource : public AudioSource {
// pin as DATA
_config.mode = i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_PDM); // Change mode to pdm if clock pin not provided. PDM is not supported on ESP32-S2. PDM RX not supported on ESP32-C3
_config.channel_format =I2S_PDM_MIC_CHANNEL; // seems that PDM mono mode always uses left channel.
//_config.use_apll = true; // experimental - use aPLL clock source to improve sampling quality
_config.use_apll = true; // experimental - use aPLL clock source to improve sampling quality
//_config.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT; // not needed
#endif
}
@@ -269,7 +269,7 @@ class I2SSource : public AudioSource {
}
DEBUGSR_PRINTF("AR: I2S#0 driver %s aPLL; fixed_mclk=%d.\n", _config.use_apll? "uses":"without", _config.fixed_mclk);
DEBUGSR_PRINTF("AR: Sample scaling factor = %6.4f\n", _sampleScale);
DEBUGSR_PRINTF("AR: %d bits, Sample scaling factor = %6.4f\n", _config.bits_per_sample, _sampleScale);
if(_config.mode & I2S_MODE_MASTER) {
if (_config.mode & I2S_MODE_PDM)
DEBUGSR_PRINTLN(F("AR: I2S#0 driver installed in PDM MASTER mode."));