Beyond sox

The manual

man sox is the authoritative reference — comprehensive, well-written, and covers every effect and flag in detail. Two companion pages are also worth bookmarking:

man sox          # effects, global options, examples
man soxformat    # format flags, encodings, file type details

LADSPA plugins

Sox can load any LADSPA plugin via the ladspa effect, which opens up hundreds of production-quality processors — noise gates, limiters, multiband compressors, pitch correction, and more:

# List installed plugins
listplugins

# Apply a plugin by label
play voice.wav ladspa <plugin-label> [params...]

On Debian/Ubuntu, apt install swh-plugins installs Steve Harris’s widely-used collection. LADSPA extends sox without changing its pipeline model.

ffmpeg handles the containers and codecs sox can’t: AAC, Opus, MP4, video tracks, streaming protocols. The two tools pair naturally — use ffmpeg to get audio into or out of awkward formats, sox for signal processing:

# Extract audio from a video, then process with sox
ffmpeg -i video.mp4 -vn audio.wav
sox audio.wav processed.wav highpass 100 norm -3

Rubber Band: high-quality time-stretching and pitch-shifting

Sox has no phase vocoder. WSOLA (tempo, pitch) is fast and reasonable, but on complex music you can hear it working. For higher-quality time-stretching, pitch-shifting, or near-unity resampling, reach for rubberband:

rubberband --tempo 1.2 input.wav output.wav   # 20% faster (same sense as sox tempo)
rubberband --time 0.8 input.wav output.wav    # 0.8x duration (--time is 1/--tempo)
rubberband --pitch 2 input.wav output.wav     # up 2 semitones (not cents)
rubberband --pitch -2 --tempo 1.1 input.wav output.wav  # combine freely

Rubber Band has two engines: R2 (default, fast, WSOLA-based) and R3 (slower, phase vocoder, noticeably better on music):

rubberband --fine --pitch 4 input.wav output.wav   # R3 engine
rubberband-r3 --pitch 4 input.wav output.wav       # equivalent

For vocal pitch-shifting, --formant preserves the formant structure so voices don’t sound cartoonish:

rubberband --fine --formant --pitch 3 voice.wav output.wav

rubberband doesn’t support stdout, so to combine with sox for format conversion, route through a temp file:

rubberband -q --pitch 2 input.wav tmp.wav && sox tmp.wav output.flac

libsox

Sox is also a C library. If you need to embed audio processing in a program, libsox exposes the full effect chain and format I/O via a C API. The header is sox.h; the source ships with examples.

What sox isn’t

Sox is a Swiss Army knife, but some problems aren’t shaped like a knife. Knowing what sox is not good at saves time:

No phase vocoder. WSOLA (tempo, pitch) works well but produces artifacts on complex material; use Rubber Band (above) when quality matters.
No multitrack routing. Sox processes one stream at a time. For independent tracks with sends and returns, look at ecasound or a DAW.
No streaming protocols. Sox reads and writes files and pipes; it has no RTSP, HLS, or WebRTC support.

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