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CLI FLAC Conversion with SoX

As I remember it, Bandcamp downloads used to come in 16bit or 24bit FLAC. It seems you don't have this choice anymore; we'll make that conversion ourselves with Sound eXchange for the sake of conserving storage space.

  1. Install SoX via homebrew:
brew install sox
  1. cd into your source FLAC album folder:
cd /Downloads/your-flac-album
  1. Convert.

This snippet will create an identically-named folder with (16-bit) appended to the end, convert the FLAC files from 24-bit to 16-bit, then finally place the converted FLAC files in the new folder:

# macOS zsh — run inside the folder with your FLACs
base="$(basename "$PWD")"
outdir="${base} (16-bit)"
mkdir -p "$outdir"

for f in *.[Ff][Ll][Aa][Cc]; do
  sr=$(soxi -r "$f")
  case "$sr" in
    44100|48000)
      # Reduce bit depth to 16-bit, keep existing sample rate
      sox -S "$f" -R -G -b 16 "$outdir/$f" dither
      ;;
    88200|176400)
      # Downsample to 44.1 kHz with high-quality, linear-phase resampler
      sox -S "$f" -R -G -b 16 "$outdir/$f" rate -v -L 44100 dither
      ;;
    96000|192000)
      # Downsample to 48 kHz with high-quality, linear-phase resampler
      sox -S "$f" -R -G -b 16 "$outdir/$f" rate -v -L 48000 dither
      ;;
    *)
      echo "Skipping $f (unsupported sample rate: $sr)"
      ;;
  esac
done
Here's the full breakdown of this command:

  1. Detects the current folder name and creates an output directory named "[folder name] (16-bit)".

  2. Iterates over all FLAC files in the folder, case-insensitively.
  3. Reads each file's sample rate using soxi.

  4. If the sample rate is 44.1 kHz or 48 kHz: converts to 16‑bit with dithering, keeping the original sample rate.

  5. If the sample rate is 88.2 kHz or 176.4 kHz: downsamples to 44.1 kHz with a very‑high‑quality, linear‑phase resampler, then converts to 16‑bit with dithering.

  6. If the sample rate is 96 kHz or 192 kHz: downsamples to 48 kHz with a very‑high‑quality, linear‑phase resampler, then converts to 16‑bit with dithering.

  7. Uses -G to guard against clipping; -S to show warnings; -R for consistent defaults.

  8. Writes outputs into the "[folder name] (16-bit)" directory with the same filenames as the originals.

  9. Skips any files with unsupported sample rates and prints a message indicating the rate.

I like to use Spek to view the audio files and compare the difference in quality.

Before:

SoX example
24-bit FLAC

After:

SoX example
16-bit FLAC

This is strictly for my personal reference—I won’t be going into any further details on SoX. May any wanderers find this useful, though!

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