Generate 1 kHz Test Tone at -20 dBFS in Audacity

This guide explains how to generate a standard 1 kHz sine wave reference tone at -20 dBFS using Audacity for broadcast audio alignment. Generating an accurate reference tone ensures audio levels match standardized broadcast delivery specifications across playback systems, mixing consoles, and transmission hardware.

Step 1: Set the Project Rate

Broadcast standards (such as EBU R128 and ATSC A/85) typically require a 48 kHz sampling rate.

1. Open Audacity.
2. In the bottom-left corner of the interface (or via Audio Setup > Audio Settings depending on your Audacity version), ensure the Project Sample Rate is set to 48000 Hz.

Step 2: Open the Tone Generator

1. Navigate to the top menu and select Generate.
2. Click Tone... to open the tone generator dialog box.

Step 3: Configure Tone Parameters

Enter the following settings to create the reference signal:

• Waveform: Select Sine.
• Frequency (Hz): Enter 1000 (which corresponds to 1 kHz).
• Amplitude: Enter 0.1. (Audacity uses a linear scale from 0.0 to 1.0 for amplitude. In digital audio, -20 dBFS equals a linear amplitude of 0.1, calculated as \(10^{(-20/20)}\).)
• Duration: Set the desired length for your alignment tone (standard broadcast line-up tones are typically 30 to 60 seconds).

Click Generate (or OK) to render the track onto the timeline.

Step 4: Verify the Output Level

1. Locate the Playback Meter at the top of the workspace.
2. Press the Spacebar to play the generated tone.
3. Observe the meter bars. Both channels (or the single mono channel) should peak steadily at exactly -20 dB.

Step 5: Export the Alignment File

1. Go to File > Export Audio...
2. Choose WAV (Microsoft) as the format.
3. Select Signed 24-bit PCM (or 16-bit PCM depending on delivery requirements).
4. Set the sample rate to 48000 Hz.
5. Save the file for use as a broadcast alignment asset.