Effects and Dynamics

Sample file — download and place in your working directory:

⬇ music.wav — “Erase Data” by Koi-discovery (CC0)

Setup:

# Varying dynamics for compand: loud / quiet / loud
sox -n _loud.wav synth 2 sawtooth 220 gain -6
sox -n _quiet.wav synth 2 sawtooth 220 gain -20
sox _loud.wav _quiet.wav _loud.wav dynamics.wav
play dynamics.wav

reverb

Simulates room acoustics. Arguments: reverberance (0–100), HF damping (0–100), room scale (0–100). Defaults are reasonable.

play music.wav reverb
play music.wav reverb 80 50 100    # large, bright room

--wet-only removes the dry signal, leaving only the wet (reverberated) signal:

play music.wav reverb --wet-only 80

Note: reverb does not extend the output file. The reverb decay is truncated at the input length. To capture the full tail, pad silence onto the end of the input first:

play music.wav pad 0 2 reverb 80

silence — trim silence

These effects need a file that actually has silence. Generate one with pad, which adds silence (in seconds) to the start and end:

sox -n padded.wav synth 5 sawtooth 220 gain -6 pad 1 1
play padded.wav

Remove leading and trailing silence:

play padded.wav silence 1 0.1 1% -1 0.1 1%

Each group is: periods duration threshold. The first group handles the start; the second (preceded by -1) handles the end.

For voice recordings, vad (voice activity detection) is simpler — it finds the onset of audio activity and trims everything before it:

play padded.wav vad

compand — dynamic range compression

compand reduces the gap between loud and quiet passages. dynamics.wav from the setup has 14 dB of range to work with.

play dynamics.wav compand 0.3,1 6:-70,-60,-20 -5 -90 0.2

Breaking that down:

• 0.3,1 — attack 0.3 s, decay 1 s
• 6:-70,-60,-20 — transfer function: input/output dB pairs
• -5 — output gain offset (reduce if sox warns about clipping)
• -90 — initial signal level
• 0.2 — delay before processing

A practical podcast leveling chain:

sox dynamics.wav podcast.wav \
    highpass 80 \
    compand 0.3,1 6:-70,-60,-20 -5 -90 0.2 \
    norm -3

Other time-based effects

Sox also provides echo (discrete delays), chorus, and flanger. Their defaults are reasonable starting points; man sox covers the tuning parameters.