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What a digital audio file is

Written 2026-10-27. Based on established audio engineering knowledge.

Yes, a digital audio file is ultimately numbers stored as bits. The detail worth knowing is what those numbers mean, and exactly where "identical to the master" stops being true.

The numbers

Most digital audio is PCM (pulse-code modulation). The signal is measured thousands of times per second, and each measurement is stored as a number.

  • Sample rate is measurements per second: 44,100 for CD, often 48,000 for video.
  • Bit depth is the precision of each measurement. At 16 bits, each sample is one of 65,536 values.
  • Channels: stereo is two of these streams interleaved.

CD audio is 44,100 × 16 × 2 ≈ 1.4 million bits per second. A WAV file is basically that list of numbers behind a small header that says how to read it.

Lossless vs lossy

  • Uncompressed (WAV, AIFF) and lossless (FLAC, ALAC): the decoded numbers are bit-for-bit identical to what went in. FLAC is like a ZIP file built for audio. "Identical to the master" is literally true here and provable with a checksum.
  • Lossy (MP3, AAC, Opus): the encoder discards what it predicts you won't hear. The decoded numbers are not the same, only perceptually close. "Sounds identical" is a claim about ears, not data.

Where the bits stop being exact

  1. The operating system may alter them. On Windows, normal ("shared") output mixes every app's sound together and can resample or rescale it. Exclusive-mode output (WASAPI exclusive, ASIO) bypasses that.
  2. The DAC (digital-to-analog converter) turns numbers into voltage. From here on, everything is analog and imperfect.
  3. Speakers, headphones and the room add the largest differences of all.

The file is exact numbers, and what you hear is an analog reproduction of them. Two identical files can sound different on two systems, and it's never the bits that differ.

Building sound from numbers

If a sound is just numbers, you can compute the numbers instead of recording them. Any program that does that is, by definition, a synthesizer. "Building from bits" and "synthesis" are the same activity. The interesting part is the model that decides what the numbers should be. See Why synth guitars sound fake.