7.9.7. AUDIO-07 — WAV File I/O

This tutorial covers reading and writing WAV files using the audio/audio_wav module, and demonstrates simple offline audio processing (reversing and amplifying).

7.9.7.1. Writing WAV Files

write_wav saves an array<float> of PCM samples as a 16-bit WAV file. Parameters are the output path, sample data, sample rate, and channel count:

require audio/audio_wav

var samples <- [for (x in range(MA_SAMPLE_RATE));
    sin(2.0 * PI * 440.0 * float(x) / float(MA_SAMPLE_RATE)) * 0.8
]
write_wav("tone.wav", samples, uint(MA_SAMPLE_RATE), 1)

The samples are stored as floating-point values in the range -1.0 to 1.0 and quantized to 16-bit integers on disk.

7.9.7.2. Reading WAV Files

read_wav loads a WAV file back into an array<float>, returning the sample rate and channel count via out-parameters. It returns true on success:

var samples : array<float>
var sample_rate : int
var channels : int
if (read_wav("tone.wav", samples, sample_rate, channels)) {
    let duration = float(length(samples)) / float(sample_rate * channels)
    print("{length(samples)} samples, {duration:.2f} seconds\n")
}

Because the file stores 16-bit integers, the round-tripped float values will have small quantization differences from the originals.

7.9.7.3. Simple Processing

With PCM data in an array<float>, any processing is just a loop over samples.

Reversing swaps samples from both ends toward the middle:

let n = length(samples)
for (i in range(n / 2)) {
    let tmp = samples[i]
    samples[i] = samples[n - 1 - i]
    samples[n - 1 - i] = tmp
}
write_wav("reversed.wav", samples, uint(sample_rate), channels)

Amplifying (or attenuating) multiplies every sample by a gain factor:

for (i in range(length(samples))) {
    samples[i] *= 0.5   // halve volume
}
write_wav("quiet.wav", samples, uint(sample_rate), channels)

The tutorial reads a gong sample from the media directory, applies each transformation, writes the result to a temporary WAV, plays both the original and processed versions for comparison, then cleans up the temporary files.

7.9.7.4. Running the Tutorial

Run from the project root:

daslang.exe tutorials/dasAudio/07_wav_io.das

The tutorial generates a 440 Hz tone and saves it to WAV, reads it back and verifies the sample values, then demonstrates reversing and volume reduction on a gong sample — playing each version so you can hear the difference.