output_bit_depth manual test

Author: FoamyGuy

tests/circuitpython-manual/audioi2sin/i2sin_record_sdcard_output_bit_depth.py

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+# SPDX-FileCopyrightText: Copyright (c) 2026 Tim Cocks for Adafruit Industries
+#
+# SPDX-License-Identifier: MIT
+
+# Record a longer I2S audio capture to a WAV file on an SD card, using the
+# `output_bit_depth` argument to have the driver downconvert each 32-bit slot
+# to signed 16-bit PCM. Compared to `i2sin_record_sdcard.py`, this avoids the
+# Python-side shift loop and writes directly from the recording buffer.
+#
+# Produces /sd/talk.wav. Set left_justified=True for SPH0645LM4H mics.
+
+import array
+import struct
+import time
+
+import board
+import sdcardio
+import storage
+import audioi2sin
+
+# ---- Recording config ------------------------------------------------------
+SAMPLE_RATE = 16000
+RECORD_SECONDS = 10
+CHUNK_SAMPLES = 1024  # samples captured per record() call
+OUTPUT_PATH = "/sd/talk.wav"
+
+# ---- Mount SD --------------------------------------------------------------
+spi = board.SPI()
+sdcard = sdcardio.SDCard(spi, cs=board.D10, baudrate=24_000_000)
+vfs = storage.VfsFat(sdcard)
+storage.mount(vfs, "/sd")
+
+# ---- Mic -------------------------------------------------------------------
+# 24-bit MEMS mics ride in 32-bit slots. Ask the driver to downconvert each
+# slot to a signed 16-bit PCM sample, so `record()` writes straight into a
+# WAV-ready 'h' buffer.
+mic = audioi2sin.I2SIn(
+    bit_clock=board.D5,
+    word_select=board.D6,
+    data=board.D9,
+    sample_rate=SAMPLE_RATE,
+    bit_depth=32,
+    output_bit_depth=16,
+    mono=True,
+    left_justified=False,  # True for SPH0645LM4H
+)
+
+actual_rate = mic.sample_rate
+print("Recording at", actual_rate, "Hz for", RECORD_SECONDS, "s ->", OUTPUT_PATH)
+
+pcm16 = array.array("h", [0] * CHUNK_SAMPLES)
+
+
+def write_wav_header(f, sample_rate, num_samples, bits_per_sample=16, channels=1):
+    byte_rate = sample_rate * channels * bits_per_sample // 8
+    block_align = channels * bits_per_sample // 8
+    data_size = num_samples * block_align
+    f.write(b"RIFF")
+    f.write(struct.pack("<I", 36 + data_size))
+    f.write(b"WAVE")
+    f.write(b"fmt ")
+    f.write(
+        struct.pack(
+            "<IHHIIHH",
+            16,  # fmt chunk size
+            1,  # PCM
+            channels,
+            sample_rate,
+            byte_rate,
+            block_align,
+            bits_per_sample,
+        )
+    )
+    f.write(b"data")
+    f.write(struct.pack("<I", data_size))
+
+
+total_samples = actual_rate * RECORD_SECONDS
+written = 0
+
+# Open with a write+read header placeholder; we'll seek back at the end to
+# patch in the real sample count.
+with open(OUTPUT_PATH, "wb") as f:
+    write_wav_header(f, actual_rate, 0)  # placeholder; rewritten below
+    start = time.monotonic()
+
+    while written < total_samples:
+        n = mic.record(pcm16, CHUNK_SAMPLES)
+        # Driver already downconverted to int16; write only the valid portion.
+        f.write(memoryview(pcm16)[:n])
+        written += n
+
+    elapsed = time.monotonic() - start
+    # Rewrite header now that we know the true sample count.
+    f.seek(0)
+    write_wav_header(f, actual_rate, written)
+
+storage.umount("/sd")
+
+print("Done. Wrote", written, "samples in", round(elapsed, 2), "s")