Time and Pitch

Four effects; two axes:

rate — resampling

Resamples the audio to a new sample rate. Pitch and duration are both preserved — the output just has fewer (or more) samples per second. Use it to change the technical format of a file, not to alter how it sounds:

sox test.wav out.wav rate 22050    # downsample to 22050 Hz
play out.wav
sox test.wav out.wav rate 48000    # upsample to 48000 Hz
play out.wav

This is equivalent to writing -r 22050 out.wav as an output format flag, but as an explicit effect it fits naturally in a chain and gives access to quality options:

• -h — high quality: longer anti-aliasing filter, better stopband rejection, audibly cleaner on music
• -v — very high quality: even longer filter; diminishing returns over -h but useful for archival or repeated resampling where rounding errors accumulate

speed — varispeed

Like a tape running faster or slower. Factor > 1 speeds up and raises pitch; < 1 slows down and lowers pitch.

play test.wav speed 1.5    # faster and higher
play test.wav speed 0.75   # slower and lower

tempo — time-stretch only

Changes duration while preserving pitch using the WSOLA algorithm (chops audio into overlapping segments and re-stitches them). Practical range: 0.5–2.0.

play test.wav tempo 1.2    # 20% faster, same pitch
play test.wav tempo 0.8    # 20% slower, same pitch

Three presets tune the algorithm for different material:

play test.wav tempo -m 1.2   # music (default)
play test.wav tempo -s 0.75  # speech
play test.wav tempo -l 1.1   # linear (least CPU, more artifacts)

pitch — pitch-shift only

Argument is in cents (100 cents = 1 semitone, 1200 = one octave).

play test.wav pitch 200     # up 2 semitones
play test.wav pitch -1200   # down one octave

pitch uses the same WSOLA algorithm as tempo — it is implemented as a tempo stretch followed by a rate resample in the opposite direction, so the duration cancels out and only the pitch shift remains. The -m/-s/-l presets are not exposed on pitch, but you can pass the same segment search overlap tuning parameters if needed.

Combining them

tempo and pitch are independent effects applied in sequence:

play test.wav tempo 1.2 pitch -400   # faster but lower

See also: Rubber Band

Sox has no phase vocoder. When quality matters — especially for time-stretching, pitch-shifting, or formant-preserved vocal shifts — rubberband is the standard tool. The “Beyond sox” chapter covers how to reach for it.