Use resampling to change a generated tone’s sample rate while keeping its duration and pitch. Use a coupled speed change when duration and pitch should move together. Use pitch-preserving stretching when the tone must fit a new length at its original frequency.

This guide is for a Mac desktop user preparing a synthetic tone for export. The worked example starts with a 10-second, 440 Hz sine wave and separates three possible requirements: deliver it at 48 kHz, shorten it with a corresponding pitch rise, or shorten it while retaining 440 Hz.

Which operation matches your intended result?

Decide what must remain fixed before opening an effect. Sample rate, duration, and tone frequency describe different properties; changing one does not always require changing the others. Audacity’s documentation explicitly distinguishes resampling, which preserves length and pitch, from changing a track’s rate, which changes both. Tracks Menu.

Your requirement Choose Expected result for the example
Deliver at 48,000 samples per second, keeping the sound’s timing and pitch Resampling or the export sample-rate setting 10 seconds, 440 Hz
Make playback 25% faster, allowing pitch to rise Coupled speed-and-pitch change 8 seconds, 550 Hz
Fit an 8-second slot while retaining the original frequency Pitch-preserving time stretching 8 seconds, nominally 440 Hz
Create a fresh steady 440 Hz tone lasting 8 seconds Generate the target tone directly 8 seconds, 440 Hz

The figures are calculated targets, not measurements from an Audacity listening test. The last row is particularly useful for this task: when the entire asset is simply a steady generated tone, you can enter the desired frequency and duration in the generator instead of processing an existing version. Audacity’s tone generator exposes both controls. Tone.

Check your Audacity version before following menu instructions

Audacity identifies 4.0.1 as its current release. Its interface differs from Audacity 3, so older instructions may name effects or controls that you cannot find. Audacity 4.0.1 Release Notes.

The current manual says that Sliding stretch replaces Audacity 3’s Change Tempo and Change Speed. The current instructions below use Audacity 4 controls; the older effect paths appear separately where useful. Sliding Stretch.

Audacity 4.0’s release notes also list Time Tracks and Play-at-speed as unavailable. Neither is needed for this workflow: use the documented track-rate controls, stretching effect, or generator to prepare the actual asset. Audacity 4.0.0 Release Notes.

Build one synthetic source with known properties

Start in a fresh project so that the example contains only the tone being processed. Open Generate → Tone and set Waveform to Sine, Frequency to 440 Hz, Amplitude (0-1) to 0.25, and Duration to 10 seconds. These are illustrative settings; Audacity documents the generator’s waveform, frequency, amplitude, and duration controls. Tone.

Read the track’s rate before doing the sample-rate example. The calculations below assume 44,100 Hz. If your generated track uses another rate, either use that value in the formulas or generate the example after setting up a 44,100 Hz project. Do not change an already generated track’s rate merely to establish the starting condition: that is itself a speed-and-pitch operation. Tracks Menu.

Keep the source project and make each alternative from that unchanged starting point. Processing the resampled version, then stretching it, then changing its rate would combine operations and make the comparison harder to interpret.

When should you resample the tone?

Choose resampling when the requirement concerns samples per second. Audacity describes it as adding or removing samples while leaving playback speed, pitch, and length unchanged. In Audacity 4, open the menu beside the track name and choose Resample track…, then specify the target rate. Tracks Menu, Audio Track Item.

For the illustrative source, 10 seconds at 44,100 Hz contains 441,000 samples per channel. A 10-second version at 48,000 Hz contains 480,000 samples per channel. The sample count changes to represent the same duration at the new rate. The intended tone frequency remains 440 Hz.

If only the delivered file needs a particular rate, you can choose that rate during export. Audacity’s export dialog includes a sample-rate control, so an explicit track-resampling step is unnecessary solely to expose that export choice. Export your audio.

Why changing the track rate gives a different result

The track menu also contains Rate:. This changes how quickly existing samples are interpreted, rather than converting their representation while preserving timing. Audacity documents that increasing the track rate shortens the audio and raises its pitch. The current track menu lists device-supported rates and provides Other… for another value. Tracks Menu, Audio Track Item.

Reinterpreting the original 441,000 samples at 48,000 Hz gives a duration of 441000 / 48000 = 9.1875 seconds. Its frequency becomes 440 × 48000 / 44100 ≈ 478.912 Hz. These calculated results explain why selecting a different track rate cannot satisfy “48 kHz, still 10 seconds, still 440 Hz.”

How do you change duration and pitch together?

A coupled speed change follows one ratio: speed multiplier = original duration / target duration. The new frequency equals the original frequency multiplied by that ratio. Audacity’s older Change Speed and Pitch documentation confirms this relationship: doubling speed halves duration and raises pitch by an octave. Change Speed and Pitch.

For a 10-second tone that must become 8 seconds, the multiplier is 10 / 8 = 1.25. That means 25% faster, giving a calculated frequency of 440 × 1.25 = 550 Hz. A 20% reduction in duration therefore requires a 25% increase in speed; the percentages use different starting quantities.

For this isolated track in Audacity 4, a documented route is to change Rate: from 44,100 Hz to 55125 Hz using Other…. The ratio 55125 / 44100 is 1.25. This changes the entire track, so reserve the route for a track whose contents should all receive the same change. Export afterward at the required delivery rate. Audio Track Item, Tracks Menu.

In Audacity 3, select the source and open Effect → Pitch and Tempo → Change Speed and Pitch. Set Speed Multiplier to 1.250, equivalently Percent Change to 25. The documented multiplier range is 0.010–50.000; those limits belong to that older effect. Change Speed and Pitch.

How do you reach eight seconds while preserving 440 Hz?

In Audacity 4, select the original tone and open Effect → Pitch and tempo → Sliding stretch. Set Initial tempo change and Final tempo change to 25%. Leave both pitch-shift controls at 0. Equal starting and finishing values make a constant change, and tempo and pitch are independent in this effect. Sliding Stretch.

The calculated target is eight seconds with the pitch retained at 440 Hz. Positive tempo changes shorten the selection. The documented tempo range is −90% to 500%, and shortening a selection can move subsequent audio earlier in its track. Use the isolated example first so later material does not complicate the result. Sliding Stretch.

For an adjustable clip edit, Audacity 4 also provides lower edge handles marked with a clock. These stretch or squeeze the clip; the upper handles trim it. A changed clip displays a speed badge that opens an exact-value field. Keep the distinction clear: trimming removes part of the displayed duration, whereas stretching changes how the retained material occupies time. Trim and stretch.

In Audacity 3, use Effect → Pitch and Tempo → Change Tempo. Its Length controls let you enter eight seconds in the to field. Enable Use high quality stretching (slow) when exact content length matters: the manual documents possible endpoint omissions or trailing silence with the default fast algorithm. Change Tempo.

When is generating a new tone the better choice?

For a plain steady sine wave, directly generating eight seconds at 440 Hz is the most straightforward recommendation. You already know every required property. Stretching becomes useful when you need to retain an existing sound’s internal sequence or edited shape while changing its total duration.

Pitch preservation does not establish that every other property remains identical. Audacity explains that independent pitch or tempo changes require resynthesis and that large changes can introduce audible artifacts. A single steady sine wave is a deliberately narrow example; it cannot establish processing quality for more complex generated material. Pitch and Tempo.

Export and check the requirement you actually chose

Open File → Export audio. For this comparison, choose WAV and the required sample rate. Use Export selected audio when exporting only the chosen tone, or Export full project audio when the project contains only the intended result. These export scopes and audio settings are documented in the current manual. Export your audio.

Check three properties separately: the intended duration, the intended tone frequency, and the exported sample rate. An eight-second result alone does not distinguish the 550 Hz coupled-speed version from the pitch-preserving version. Likewise, a 48 kHz file does not tell you whether its track was first reinterpreted at a different rate.

Choose the operation by the property that must change, then preserve the others deliberately. For this generated-tone task, resample for delivery requirements, use coupled speed changes for linked timing and pitch movement, and stretch when existing material must keep its pitch at a new length. Generate the final tone directly when frequency and duration fully describe the asset.

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