CLI Overview

minimodem is a command-line software audio FSK modem for encoding and decoding digital data using frequency-shift keying over audio channels.

Basic Syntax

minimodem [--tx|--rx] [options] {baudmode}

Command Structure

The minimodem command consists of three main components:

Mode flag: Specify transmit (--tx) or receive (--rx) mode
Options: Various configuration flags and parameters
Baudmode: The data rate and protocol specification

Mode Selection

You must specify either transmit or receive mode:

minimodem --tx 1200

Receive mode (--rx) is the default if no mode is specified.

Quick Start Examples

Send Data

echo "Hello World" | minimodem --tx 1200

Transmit text at 1200 baud using audio output

Receive Data

minimodem --rx 1200

Receive and decode 1200 baud audio input

File Input

minimodem --rx --file audio.wav 1200

Decode data from an audio file

Custom Frequencies

minimodem --tx -M 1200 -S 2200 1200

Transmit with custom mark and space frequencies

Command-Line Flags

All options can be specified using short or long form:

Short	Long	Description
`-t`	`--tx`, `--transmit`, `--write`	Transmit mode
`-r`	`--rx`, `--receive`, `--read`	Receive mode (default)
`-f`	`--file {filename}`	Read from or write to audio file
`-q`	`--quiet`	Suppress status messages
`-V`	`--version`	Display version information

Input/Output

Transmit
Receive

minimodem in transmit mode reads data from stdin and outputs audio:

# From a file
cat message.txt | minimodem --tx 1200

# Interactive typing
minimodem --tx 1200
# Type your message and press Ctrl+D to end

# To an audio file
echo "test" | minimodem --tx --file output.wav 1200

minimodem in receive mode captures audio input and writes decoded data to stdout:

# From microphone to terminal
minimodem --rx 1200

# From audio file to file
minimodem --rx --file input.wav 1200 > decoded.txt

# Pipe to another command
minimodem --rx 1200 | grep "pattern"

Audio Backends

minimodem supports multiple audio systems:

System Default

By default, minimodem uses your system’s default audio interface (ALSA, PulseAudio, or sndio depending on your system).

minimodem --rx 1200

ALSA

Direct ALSA device access:

minimodem --rx --alsa 1200
minimodem --rx --alsa=plughw:1,0 1200

sndio

OpenBSD sndio support:

minimodem --rx --sndio 1200
minimodem --rx --sndio=snd/0 1200

Audio Files

Read from or write to WAV/FLAC files:

minimodem --rx --file recording.wav 1200
minimodem --tx --file output.flac 300

Status Messages

When not in quiet mode, minimodem displays status information to stderr:

### CARRIER 1200 @ 1200.0 Hz ###
[decoded data appears here]
### NOCARRIER ndata=42 confidence=2.145 ampl=0.850 bps=1200.00 ###

CARRIER: Signal detected and decoding started
NOCARRIER: Signal lost or transmission ended
confidence: Signal quality metric
ampl: Signal amplitude
bps: Actual detected bit rate

Exit Status

Code	Meaning
0	Success
1	Error (invalid arguments, audio device failure, etc.)

Modes

Transmit and receive modes

Baud Modes

Available protocols and speeds

Options

Complete options reference

Command Reference

Basic Syntax

Command Structure

Mode Selection

Quick Start Examples

Send Data

Receive Data

File Input

Custom Frequencies

Command-Line Flags

Input/Output

Audio Backends

Status Messages

Exit Status

See Also

Modes

Baud Modes

Options

Build docs developers (and LLMs) love

Command Reference

​Basic Syntax

​Command Structure

​Mode Selection

​Quick Start Examples

Send Data

Receive Data

File Input

Custom Frequencies

​Command-Line Flags

​Input/Output

​Audio Backends

​Status Messages

​Exit Status

​See Also

Modes

Baud Modes

Options

Build docs developers (and LLMs) love

Basic Syntax

Command Structure

Mode Selection

Quick Start Examples

Command-Line Flags

Input/Output

Audio Backends

Status Messages

Exit Status

See Also