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Fix(ESP32): Correct PDM DAC clock configuration #81

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Fix(ESP32): Correct PDM DAC clock configuration #81

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Fix(ESP32): Correct PDM DAC clock configuration
Meshwa428 Oct 14, 2025
bb1ef3a
Merge branch 'earlephilhower:master' into master
Meshwa428 Oct 14, 2025
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18 changes: 6 additions & 12 deletions src/ESP32PDMAudio.h
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Original file line number Diff line number Diff line change
Expand Up @@ -66,15 +66,9 @@ class ESP32PDMAudio : public ESP32I2SAudio {
@return True if succeeded
*/
bool setFrequency(int freq) override {

// TODO - There is some fixed off-by-ratio 1/1.25 in the PDM output clock vs. the PCM input data at IDF 5.5
freq *= 8;
freq /= 10;
if (_running && (_sampleRate != freq)) {
i2s_pdm_tx_clk_config_t clk_cfg;
clk_cfg = I2S_PDM_TX_CLK_DEFAULT_CONFIG((uint32_t)freq);
clk_cfg.up_sample_fp = 960;
clk_cfg.up_sample_fs = 480;
// [FIX] Use the correct clock configuration for DAC-style PDM output.
i2s_pdm_tx_clk_config_t clk_cfg = I2S_PDM_TX_CLK_DAC_DEFAULT_CONFIG((uint32_t)freq);
i2s_channel_disable(_tx_handle);
i2s_channel_reconfig_pdm_tx_clock(_tx_handle, &clk_cfg);
i2s_channel_enable(_tx_handle);
Expand Down Expand Up @@ -104,9 +98,10 @@ class ESP32PDMAudio : public ESP32I2SAudio {
chan_cfg.dma_frame_num = _bufferWords;
assert(ESP_OK == i2s_new_channel(&chan_cfg, &_tx_handle, nullptr));

// [FIX] Use the specific PDM DAC configurations for both clock and slot.
i2s_pdm_tx_config_t pdm_cfg = {
.clk_cfg = I2S_PDM_TX_CLK_DEFAULT_CONFIG(_sampleRate),
.slot_cfg = I2S_PDM_TX_SLOT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_STEREO),
.clk_cfg = I2S_PDM_TX_CLK_DAC_DEFAULT_CONFIG(_sampleRate),
.slot_cfg = I2S_PDM_TX_SLOT_DAC_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_STEREO),
.gpio_cfg = {
.clk = I2S_GPIO_UNUSED,
.dout = (gpio_num_t)_dout,
Expand All @@ -116,9 +111,8 @@ class ESP32PDMAudio : public ESP32I2SAudio {
},
},
};
// The slot configuration must be set to output PCM data for the hardware modulator.
pdm_cfg.slot_cfg.data_fmt = I2S_PDM_DATA_FMT_PCM;
pdm_cfg.clk_cfg.up_sample_fp = 960;
pdm_cfg.clk_cfg.up_sample_fs = 480;
assert(ESP_OK == i2s_channel_init_pdm_tx_mode(_tx_handle, &pdm_cfg));

i2s_chan_info_t _info;
Expand Down