I am trying to perform simple audio denoising using an STM32F401RE Nucleo board.

I have .wav audio files that are:

• mono

• 16-bit PCM

• 16 kHz

• about 7–8 seconds long

Python reads the audio samples and sends them one by one over UART to the STM32.
The STM32 applies a simple moving-average filter and sends the processed samples back to Python.
Python then reconstructs the filtered samples into a new .wav file.

However the reconstructed audio file is incorrect:

• it becomes only about 2–4 seconds long

• the output audio contains mostly noise/glitches instead of speech

Example output from Python:

Total samples in file: 130672
Filtered samples received: 72021

So it seems that many samples are lost during UART transmission or processing.

I want to understand how to correctly stream audio samples over UART to STM32 without losing data.

STM32 Code (filter + UART processing)

uint8_t rx_char;
uint8_t buffer[50];
uint8_t index = 0;

int16_t x0 = 0;
int16_t x1 = 0;
int16_t x2 = 0;
int16_t x3 = 0;

HAL_UART_Receive(&huart2, &rx_char, 1, HAL_MAX_DELAY);

if(rx_char == '\r' || rx_char == '\n')
{
    buffer[index] = '\0';

    int16_t value = (int16_t)atoi((char*)buffer);

    x3 = x2;
    x2 = x1;
    x1 = x0;
    x0 = value;

    int32_t sum = (2*(int32_t)x0 + (int32_t)x1 + (int32_t)x2);
    int16_t result = sum / 4;

    char msg[50];
    sprintf(msg,"\r\nResult: %d\r\n\r\n",result);

    HAL_UART_Transmit(&huart2,(uint8_t*)msg,strlen(msg),HAL_MAX_DELAY);

    memset(buffer,0,sizeof(buffer));
    index = 0;
}
else
{
    if(index < 49)
        buffer[index++] = rx_char;
}

Python Code

import wave
import numpy as np
import serial
import time

ser = serial.Serial('COM9',115200,timeout=1)

filtered_samples = []

file_path = r"recordings/raw_enrollment_16k/user_1/sample_1.wav"

with wave.open(file_path,'rb') as w:
    frames = w.readframes(w.getnframes())
    samples = np.frombuffer(frames,dtype=np.int16)

print("Total samples in file:", len(samples))

for s in samples:

    ser.write((str(int(s)) + "\n").encode())

    time.sleep(0.0005)

    while ser.in_waiting:
        response = ser.readline().decode(errors='ignore').strip()

        if response:
            try:
                value = int(response.split()[-1])
                filtered_samples.append(value)
            except:
                pass

print("Filtered samples received:", len(filtered_samples))