Getting Started

Check your install

sox --version

You should see a version line. If it starts with SoX_ng, you have the maintained fork; if it says SoX 14.4.2, you have the 2015 legacy release. The book works on both — a few sox_ng-only features are flagged where they come up.

Inspecting files with soxi

soxi reads metadata without touching the audio. The book ships with a short voice recording you can try it on:

⬇ voice.wav (CC0)

soxi voice.wav

Input File     : 'voice.wav'
Channels       : 1
Sample Rate    : 48000
Precision      : 16-bit
Duration       : 00:00:04.09 = 196162 samples ~ 306.503 CDDA sectors
File Size      : 392k
Bit Rate       : 768k
Sample Encoding: 16-bit Signed Integer PCM

Useful individual fields (handy in shell scripts):

soxi -r voice.wav    # sample rate
soxi -b voice.wav    # bit depth
soxi -c voice.wav    # channels
soxi -D voice.wav    # duration in seconds

A test tone

When you want predictable audio to experiment with, generate it:

sox -n test.wav synth 10 sine 440 gain -6
play test.wav

Three new pieces, one sentence each: -n in the input position means “no input file — generate audio instead.” synth 10 sine 440 synthesizes ten seconds of a 440 Hz sine wave. gain -6 knocks it down 6 dB (roughly half amplitude), which leaves headroom so later effects don’t clip. Chapter 10 goes deeper on synth; this is all you need for now.

Playing audio with play

play test.wav

play is sox with your speaker as the implicit output. It is literally a symlink to the same binary. It needs a working audio device — on headless servers, use sox ... -n with stat or soxi to verify results instead.

Scale the playback amplitude with -v (1.0 = unchanged, 0.5 = half amplitude). Despite the name, -v operates on amplitude, which is linear — halving the amplitude reduces perceived loudness by 6 dB, not by half. Use gain (chapter 3) if you want to think in decibels:

play -v 0.5 test.wav

Play only the first half-second:

play test.wav trim 0 0.5

That trim 0 0.5 at the end is an effect. Don’t worry about the syntax yet — chapter 2 will make it click.

Recording with rec

rec is the mirror image: sox with your microphone as the implicit input.

rec capture.wav              # record until Ctrl-C
rec capture.wav trim 0 5     # record for 5 seconds