Generate Frequency Sweeps in Audacity: Log vs Linear

Audacity fully supports the creation of both linear and logarithmic frequency sweeps through its built-in Chirp generator. This guide explains how to generate these sweeps step-by-step, highlights the fundamental differences between linear and logarithmic frequency progression, and details when to choose each scale for audio testing, room calibration, or sound design.

How to Generate a Frequency Sweep in Audacity

Audacity uses the term "Chirp" to describe an audio signal whose frequency changes over time.

1. Open Audacity.
2. Navigate to the top menu and select Generate > Chirp....
3. Choose your desired Waveform (Sine is the standard choice for frequency testing).
4. Enter the Start Frequency (Hz) and End Frequency (Hz) (for example, 20 Hz to 20,000 Hz for full-range audio).
5. Set the Start Amplitude and End Amplitude (a setting of 0.8 is typical to prevent digital clipping).
6. Under the Interpolation drop-down menu, choose either Linear or Logarithmic.
7. Set the Duration of the sweep.
8. Click Generate to create the track.

Linear vs. Logarithmic Sweeps

The key difference between the two scales lies in the Interpolation setting, which governs how the frequency transitions from the start value to the end value.

Linear Frequency Sweeps

In a linear sweep, the frequency changes at a constant rate in Hertz per second. For example, during a 10-second sweep from 0 Hz to 10,000 Hz, the signal increases by 1,000 Hz every second.

• Behavior: The sweep spends the vast majority of its duration in the high-frequency range because human hearing perceives pitch logarithmically. The jump from 100 Hz to 200 Hz is an entire octave, but represents only a fraction of a second in a linear sweep.
• Common Uses: Synthesizer effects, educational demonstrations of waveform mathematics, and certain RF (radio frequency) testing scenarios.

Logarithmic Frequency Sweeps

In a logarithmic (or exponential) sweep, the frequency changes by a constant number of octaves per second. The sweep doubles in frequency at fixed time intervals (e.g., 20 Hz to 40 Hz takes the same amount of time as 10,000 Hz to 20,000 Hz).

• Behavior: A logarithmic sweep sounds like a smooth, steady rise across the entire audible spectrum to human ears, giving equal auditory weight to bass, midrange, and treble frequencies.
• Common Uses: Acoustic measurements, speaker testing, room impulse response deconvolution, and audio equipment frequency response checks.