Audacity DTMF Tones: Customizable Parameters

Audacity includes a built-in generator for Dual-Tone Multi-Frequency (DTMF) tones, the audio signals generated when pressing buttons on standard telephone keypads. This guide provides a direct breakdown of every parameter you can customize when generating DTMF keypad tones within the software.

To access these settings in Audacity, open the Generate menu from the top toolbar and select DTMF Tones.... The dialog box presents several configurable parameters:

Sequence

The Sequence field defines the actual characters to be translated into audio tones. Audacity accepts standard keypad values, including:

• Numeric digits: 0 through 9
• Standard symbols: * (star) and # (hash/pound)
• Special signaling characters: A, B, C, and D (used in military and legacy telecommunications switching systems)

Audacity will generate tone pairs in the exact order entered in this text field.

Tone Duration

The Tone duration setting specifies how long each individual DTMF tone sounds.

• It is measured in milliseconds (ms) or seconds, depending on the current time format.
• Standard telecom equipment typically requires tones to sound for at least 40 to 50 milliseconds to be reliably recognized by automated decoders.

Silence Duration

The Silence duration parameter dictates the length of the silent gap inserted between each consecutive tone in the sequence.

• Like tone duration, this is measured in milliseconds or seconds.
• A standard inter-digit pause of 40 to 100 milliseconds is commonly used to ensure automated receivers do not interpret two identical consecutive numbers as a single tone.

Duty Cycle

Certain versions of the DTMF generator allow you to define the ratio between tone duration and silence duration as a Duty cycle percentage.

• A higher duty cycle means the tone plays longer relative to the silence that follows.
• A 50% duty cycle provides an equal duration for both tone playback and inter-digit silence.

Duration / End Selection

The bottom of the dialog includes the standard Audacity time control box, indicating the Total Duration or target audio length. Adjusting the tone duration, silence duration, and sequence length will automatically update the overall duration of the generated audio track.