sox (Sound eXchange) - CLI Audio Toolkit

Overview of sox for recording and processing audio on macOS, including installation, usage, and common commands.

Table of Contents
SoX - Sound eXchange
sourceforge.net
https://sourceforge.net/projects/sox

What is sox?

sox (Sound eXchange) is a command-line utility for audio recording, editing, processing, and format conversion. It works natively with macOS CoreAudio and is highly useful when paired with virtual audio devices like BlackHole or Loopback.

Installation

Install via Homebrew:

brew install sox

For MP3 support, use FFmpeg:

brew install ffmpeg

Record Audio from Devices

Record from the built-in microphone:

sox -t coreaudio "External Microphone" mic.wav

Record system audio routed through a virtual device like BlackHole:

sox -t coreaudio "BlackHole 16ch" system.wav

You don’t have to use BlackHole, but you need a virtual audio device to record system audio separately, because macOS does not allow direct capture of system output natively.

Record both simultaneously:

sox -t coreaudio "BlackHole 16ch" system.wav & 
sox -t coreaudio "Built-in Microphone" mic.wav

To stop: Ctrl+C (foreground) or kill %1 (background).

Check if a Recording is Running

ps aux | grep sox

Stop all sox recordings:

pkill sox

Basic Audio Processing Examples

Trim and fade:

sox input.wav output.wav trim 0 30 fade 0.5 30 0.5

Normalize volume:

sox input.wav output.wav norm

Convert format:

sox input.wav output.mp3

Tips

  • Use ffmpeg -f avfoundation -list_devices true -i "" to list macOS audio devices.
  • Combine with sox --combine merge for multi-channel outputs.
  • Diarization and more advanced labeling requires external tools (e.g., Whisper + pyannote).

Reference

  • Official site: http://sox.sourceforge.net/
  • man sox or sox --help for full command list.

links

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