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I2S recoding to SD card choppy (with esp32-s3 and INMP441) #2122
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Hello @pschatzmann et al,
Could you please tell me what I am doing wrong in the code below. This captures speech, but the recording has audible glitches at irregular intervals - sample recording here.
Screenshot 2025年08月06日 at 9 08 16 AM
This is with an esp32-s3 and INMP441, with latest arduino-esp32 and arduino-audio-tools from GitHub.
#include <AudioTools.h>
#include <FS.h>
#include <SD_MMC.h>
#define MIC_SD 2
#define MIC_WS 3
#define MIC_SCK 4
#define SD_CLK 12
#define SD_CMD 11
#define SD_D0 13
File file;
I2SStream micStream;
//ConverterFillLeftAndRight<int16_t> left_and_right(RightIsEmpty);
//ConverterStream<int16_t> converter(micStream, left_and_right);
EncodedAudioStream encoder(&file, new WAVEncoder());
StreamCopy copier;
bool recording = false;
uint32_t startTime;
void setup() {
Serial.begin(115200);
initSd();
startRecording("/test.wav");
recording = true;
startTime = millis();
}
void loop() {
if (recording) {
copier.copy();
if (millis()-startTime > 5000) {
stopRecording();
recording = false;
Serial.println("Finished");
}
}
}
bool initSd() {
if (!SD_MMC.setPins(SD_CLK, SD_CMD, SD_D0)) {
Serial.println("SD_MMC.setPins() failed");
return false;
}
if (!SD_MMC.begin("/sdcard", true)) {
Serial.println("SD_MMC.begin() failed");
return false;
}
return true;
}
bool startRecording(const char* fn) {
file = SD_MMC.open(fn, FILE_WRITE);
if (!file) {
Serial.println("SD_MMC.open() failed");
return false;
}
auto cfg = micStream.defaultConfig(RX_MODE);
cfg.sample_rate = 22050;
cfg.channels = 1;
cfg.channel_format = I2SChannelSelect::Left;
cfg.bits_per_sample = 16;
cfg.pin_bck = MIC_SCK;
cfg.pin_ws = MIC_WS;
cfg.pin_data = MIC_SD;
if (!micStream.begin(cfg)) {
Serial.println("micStream.begin() failed");
file.close();
return false;
}
if (!encoder.begin(cfg)) {
Serial.println("encoder.begin() failed");
file.close();
return false;
}
//copier.begin(encoder, converter); // didn't make a difference
copier.begin(encoder, micStream);
return true;
}
void stopRecording() {
micStream.end();
encoder.end();
copier.end();
file.close();
}
Thank you for your time and patience.
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I did some tests (both with ESP 3.3.0 and ESP 3.2.1 ) with the AudioKit using this sketch and could not reproduce your issue:
The AudioBoardStream is just an I2SStream that also sets up the codec chip.
ps. I also made some tests with your sketch and ended up with empty files. To correct this, I made sure
- to delete the file before the processing with SD.remove(fn);
- commented out the cfg.buffer_size and cfg.buffer_count
- changed stopRecording() to
void stopRecording() { // close file first and print file size file.close(); file = SD.open(fn, FILE_READ); Serial.print("File Size: "); Serial.println(file.size()); file.close(); micStream.end(); encoder.end(); copier.end(); }
Replies: 3 comments 12 replies
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Please follow the recommendations diven here!
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The waveform looks clean when I plot the microphone data via serial, @pschatzmann . (Screen recording) What could make a difference when writing it to the SD card instead?
Here the code I used, for reference:
#include "AudioTools.h"
#define MIC_SD 2
#define MIC_WS 3
#define MIC_SCK 4
I2SStream i2sStream;
CsvOutput<int32_t> csvOutput(Serial);
StreamCopy copier(csvOutput, i2sStream);
void setup(void) {
Serial.begin(115200);
AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Info);
auto cfg = i2sStream.defaultConfig(RX_MODE);
cfg.sample_rate = 22050;
cfg.channels = 1;
cfg.channel_format = I2SChannelSelect::Left;
cfg.bits_per_sample = 16;
cfg.pin_bck = MIC_SCK;
cfg.pin_ws = MIC_WS;
cfg.pin_data = MIC_SD;
i2sStream.begin(cfg);
csvOutput.begin(cfg);
}
void loop() {
copier.copy();
}
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Then test the SD write speed: it needs to be higher than the generated i2s data!
You can try to increase the SPI frequency...
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I did most of my testing on 3.3.0, but I also tried with 3.2.1 and 3.1.3 once. (3.1.3 showed some unrelated issue, which made me believe that at least my downgrading had worked.)
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Did you try with the same parameters like in the Python example (pins, BUFFER_LENGTH_IN_BYTES, SPI frequency) ?
I will try to do a test with 3.3.0 on an AudioKit later today...
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It's on slightly different hardware (S2 rather than S3), but I used arbitrary GPIOs pins for I2S for both.
BUFFER_LENGTH_IN_BYTES ... how would I set the equivalent in arduino-audio-tools? (Increasing I2S_BUFFER_COUNT to 16-20 and/or I2S_BUFFER_SIZE to 1024 in AudioToolsConfig.h didn't make a difference when I tried. Is there anything else? I tried giving the copier a larger buffer size at some point as well.)
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cfg.buffer.size = 1024; cfg.buffer_count = 40;
Not sure what SD API the Python example is using: Did you try with the SD.h library instead of SDMMC ?
Your test skech sine recording sketch showed that the I2S was working properly: so the issue must come from the interaction of I2S and the SD...
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Now using the same hardware (S2) and same pins, and it still glitches for me with Arduino 🤨 Increasing the buffer size and count in the way you described didn't fix it either, unfortunately.
On the S2 I ended up using SD, since it lacks the MMC hardware peripheral.
Here is my current test sketch fwiw:
#include <AudioTools.h> #include <FS.h> #include <SD.h> #include <SPI.h> #define MIC_SD 2 #define MIC_WS 3 #define MIC_SCK 4 #define SD_SCK 14 #define SD_MOSI 13 #define SD_MISO 12 #define SD_CS 11 File file; I2SStream micStream; EncodedAudioStream encoder(&file, new WAVEncoder()); StreamCopy copier; bool recording = false; uint32_t startTime; void setup() { Serial.begin(115200); initSd(); startRecording("/test.wav"); recording = true; startTime = millis(); } void loop() { if (recording) { copier.copy(); if (millis()-startTime > 5000) { stopRecording(); recording = false; Serial.println("Finished"); } } } bool initSd() { // using SPI on ESP32-S2 if (!SPI.begin(SD_SCK, SD_MISO, SD_MOSI, SD_CS)) { Serial.println("SPI.begin() failed"); return false; } if (!SD.begin(SD_CS)) { Serial.println("SD.begin() failed"); return false; } return true; } bool startRecording(const char* fn) { file = SD.open(fn, FILE_WRITE); if (!file) { Serial.println("SD.open() failed"); return false; } auto cfg = micStream.defaultConfig(RX_MODE); cfg.sample_rate = 22050; cfg.channels = 1; cfg.channel_format = I2SChannelSelect::Left; cfg.bits_per_sample = 16; cfg.pin_bck = MIC_SCK; cfg.pin_ws = MIC_WS; cfg.pin_data = MIC_SD; cfg.buffer_size = 1024; cfg.buffer_count = 40; if (!micStream.begin(cfg)) { Serial.println("micStream.begin() failed"); file.close(); return false; } if (!encoder.begin(cfg)) { Serial.println("encoder.begin() failed"); file.close(); return false; } copier.begin(encoder, micStream); return true; } void stopRecording() { micStream.end(); encoder.end(); copier.end(); file.close(); }
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I did some tests (both with ESP 3.3.0 and ESP 3.2.1 ) with the AudioKit using this sketch and could not reproduce your issue:
The AudioBoardStream is just an I2SStream that also sets up the codec chip.
image
ps. I also made some tests with your sketch and ended up with empty files. To correct this, I made sure
- to delete the file before the processing with SD.remove(fn);
- commented out the cfg.buffer_size and cfg.buffer_count
- changed stopRecording() to
void stopRecording() { // close file first and print file size file.close(); file = SD.open(fn, FILE_READ); Serial.print("File Size: "); Serial.println(file.size()); file.close(); micStream.end(); encoder.end(); copier.end(); }
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