To make a sustained loop in Audacity on a Mac, generate a steady tone with a whole number of waveform cycles, select its exact duration, and enable loop playback. If your generated sound has mismatched ends, move that join into the middle and crossfade it before exporting.

This walkthrough creates an original four-second synthetic tone and turns it into a reusable loop. The menu instructions follow the current Audacity 4 documentation; Audacity lists version 4.0.1 as its current release. Use menu commands where shown, since shortcuts and layouts can differ between versions. Audacity Changelog

What makes a generated sound loop seamlessly?

A loop connects the end of an audio selection directly to its beginning. For a steady sine tone, that connection should continue the waveform’s existing pattern. An abrupt change at the boundary can produce a click; a recurring change in level can make the sound pulse instead of sustain.

Audacity’s loop control repeats a timeline region during playback. It does not edit the samples at the boundary. Preparing the audio and enabling repetition are therefore separate steps. Transport

For a single steady tone, use this calculation: frequency in Hz × duration in seconds = number of cycles. Choose a duration that produces a whole number of cycles and can be represented by a whole number of samples at the project sample rate. This is a mathematical design rule for periodic audio, rather than an automatic Audacity setting.

Illustrative tone Duration Cycles Design implication
220 Hz 4 seconds 880 A whole-cycle boundary
441 Hz 4 seconds 1,764 Also a whole-cycle boundary
220.3 Hz 4 seconds 881.2 The boundary interrupts a cycle

At 48,000 samples per second, four seconds contains 192,000 samples. For the 220 Hz example, repeating those samples continues the ideal sine pattern. The last stored sample need not equal the first: it should lead into the first with the same step the waveform would naturally take next. A deterministic calculation confirms that relationship; it is not an Audacity playback or listening test.

This rule assumes a constant frequency and amplitude. After edits that change the beginning or ending, check the resulting sound again rather than relying on the original calculation.

Generate the four-second source tone

Start with a new project containing no other audio. For the worked example, set the sample rate for new projects to 48000 in Audacity → Preferences → Audio settings, then create the project. The official reference identifies this preference as the sample rate used for new projects. Audio settings

Place the cursor at time zero and open Generate → Tone. Enter these illustrative settings:

Control Value
Waveform Sine
Frequency 220 Hz
Amplitude (0–1) 0.3
Duration Four seconds

Apply the generator. Audacity documents these controls and generates audio from the selection’s beginning, or from the cursor when nothing is selected. The amplitude setting is a waveform level, with 1 representing full scale; 0.3 is simply the chosen value for this example. Tone

Keep this first version steady throughout. A fade at each outer edge would introduce a repeated reduction in level, changing the sustained character you are trying to create. Save an editable project before experimenting with further processing.

If you want another basic timbre later, the generator also offers other waveforms, including Triangle and Square, no alias. Complete the sine example first so you have a simple reference for identifying boundary problems. Tone

Select the exact loop and check repeated playback

Select some audio in the waveform, then use the bottom toolbar to enter a selection start of zero and an end of four seconds. Audacity’s Selection start, end and Duration readouts are editable; their formats include clock time and samples. For this 48 kHz example, a sample-based selection runs from sample position 0 to 192000. Bottom toolbar

Set up playback in this order:

  1. Keep the exact four-second time selection active.
  2. Choose Select → Looping → Set loop region to selection.
  3. Enable the transport’s Toggle Loop Region button if it is inactive.
  4. Press Play and let the region repeat several times.

The selection command defines the region, while the transport toggle enables its repeated playback. Audacity also provides Select → Looping → Set loop region in/out for entering the loop’s start and end directly. Select, Transport

Listen specifically as playback crosses from the end back to the beginning. Check for a click, a pause or a recurring dip in level. These are checks for you to perform on your project; no listening result is assumed here.

For an additional visual check, copy the complete selection and paste it immediately after the original in a temporary project. Inspect the join at four seconds at a close zoom. Compare its waveform spacing and shape with neighboring cycles. Audacity documents Edit → Copy as preserving the source and Edit → Paste as inserting the clipboard audio at the cursor. Edit

How do you repair a generated sound with mismatched ends?

If you have already shaped a generated sound and want to retain it, use a midpoint rearrangement. The idea is to move the original end-to-start mismatch into the middle, where a crossfade can reach both sides. The new outer boundary then reconnects samples that were neighbors at the original midpoint.

The following is an editing method derived from Audacity’s documented copy, paste and crossfade operations. It suits a sustained source with a continuous middle. It does not make a changing pitch or level become constant.

Move the old boundary into the middle

For an illustrative source spanning zero to four seconds, preserve the original project and assemble a working copy in a separate project:

  1. In the source, select exactly two to four seconds and choose Edit → Copy.
  2. In the working project, place the cursor at zero and choose Edit → Paste.
  3. Return to the source and copy exactly zero to two seconds.
  4. In the working project, place the cursor at two seconds, with no time range selected, and paste.

The working sequence is now the original second half followed by the original first half. Before proceeding, confirm there is no gap or overlap at two seconds. Numeric selection readouts help preserve the exact midpoint. The clipboard operations leave the original source intact. Edit, Bottom toolbar

Crossfade the internal mismatch

Select a short region centered on the new two-second join. As an illustrative starting point, select 1.950 to 2.050 seconds: 50 milliseconds on either side. Apply Effect → Fading → Crossfade clips. Audacity blends the selected end of one clip with the selected beginning of the next; the effect has no adjustable parameters. Crossfade Clips

If the pasted pieces form continuous audio without a split, the manual documents that the effect crossfades the selection’s first and second halves instead. Its limits still apply: select no more than two clips per channel, and keep both selection boundaries inside audio. Crossfade Clips

Treat the suggested selection length as a starting point. If the blend produces a noticeable level change, undo it and try another length. Crossfading phase-mismatched tones can change their combined amplitude; a longer blend does not automatically improve a steady tone.

After processing, measure the resulting audio extent again and redefine the loop around it. Do not assume the original four-second duration remains appropriate. Check both the internal blend and the outer repeat boundary.

For a workflow with explicitly overlapping tracks and selectable fade curves, Audacity provides Effect → Fading → Crossfade tracks. Its Constant Gain setting suits correlated material, while its constant-power shapes suit unrelated material. Neither option guarantees a transparent result for arbitrary phase relationships. Crossfade Tracks

Export one loop unit and verify the file

Once the loop works, select its exact audio extent and open File → Export audio. Choose Export selected audio, or choose Export audio in loop region when that region exactly matches the finished unit. The current export documentation distinguishes both from Export full project audio. Export your audio

For this example, choose WAV, mono if the source is mono, and the same 48000 sample rate. Use PCM encoding, such as Signed 16-bit PCM. Audacity documents PCM WAV as uncompressed audio and exposes channel, sample-rate and encoding controls. WAV Export Options

Import the exported file into a separate project and repeat the boundary check using that file’s actual extent. Importing adds a file as a new track, so a separate project keeps your verification copy easy to identify. Import

A loopable audio file still needs a playback application that repeats it without an inserted pause. Test it in the intended destination as well as Audacity. If you instead need a fixed-length sustained file, assemble consecutive copies of the verified unit before exporting that longer sequence.

Diagnose the remaining problem

What you notice First check Next action
A click at each wrap Frequency, duration and selection boundaries Restore the calculated whole-cycle selection or repair the mismatch
A regular drop in level Outer fades or cancellation inside a blend Restore steady edges; revise the crossfade
A pause between repetitions Empty time inside the loop region Set the region to the exact audio extent
Repetition of the wrong passage A loop region left from an earlier edit Reset it from the current selection
The export includes extra material Export type and selected extent Export only the verified unit

For a newly generated steady tone, begin with the calculated whole-cycle method. Use the midpoint crossfade when preserving an altered source matters more than retaining its original duration. Finish by checking the exported unit across several repeats, so the file you keep is the same one you have verified.

Sources