Basic Effects

trim — cut out a section

play test.wav trim start [length]

trim takes a start position and a length, not start and end.

play test.wav trim 0 5      # first 5 seconds
play test.wav trim 3 4      # 4 seconds starting at 3s
play test.wav trim 5        # skip the first 5 seconds
play test.wav trim -3       # last 3 seconds
play test.wav trim 00:01:30 # start at 1m30s

reverse — play backwards

play test.wav reverse

Sox loads the whole file into memory to do this; large files are slow.

fade — smooth edges

play test.wav fade [type] fade-in [duration] fade-out

The type can be q (quarter-sine, natural sounding), t (linear), h (half-sine), or l (logarithmic). Omitting type defaults to linear.

play test.wav fade 1         # 1s linear fade-in, play to end
play test.wav fade q 2 0 2   # 2s fade-in, full duration, 2s fade-out

Duration 0 means “play to the natural end of the file.”

vol and gain — adjust volume

vol takes a multiplier; gain takes decibels:

play test.wav vol 0.5    # half amplitude
play test.wav vol 2.0    # double (can clip!)
play test.wav gain -6    # quieter by 6 dB
play test.wav gain 6     # louder by 6 dB (can clip!)

A rough guide: −6 dB ≈ half perceived loudness; +6 dB ≈ double.

sox_ng 14.5+: vol accepts a second argument that enables a soft-clipping limiter so boosts don’t hard-clip when they exceed 0 dBFS. See man sox for the exact argument. On legacy sox, vol 2 clips; on sox_ng with the limiter, it shapes the peak instead.

norm — automatic normalization

norm brings the peak sample to a target level (default 0 dBFS):

play test.wav norm       # peak to 0 dBFS
play test.wav norm -3    # peak to -3 dBFS (safer headroom)

To save the result: sox test.wav out.wav norm -3.

stat — measure levels

Use -n as the output to discard audio and just print statistics:

sox test.wav -n stat     # linear amplitudes, whole file mixed to mono
sox test.wav -n stats    # dB levels, per-channel columns

stats is generally more useful: it reports in dB and breaks out each channel separately. stat reports linear amplitude values, which are harder to interpret. Both print to stderr.