Sample Pitch & Time-Stretch Calculator

Playing a recording faster makes it higher and shorter. Playing it slower makes it lower and longer. That is how a turntable, a tape machine and the keyboard of a sampler behave, and it is the idea behind many hip-hop and electronic production tricks. The numbers that connect pitch, speed, tempo and length all follow from one formula, which this calculator applies in three directions.

The formula

Each semitone multiplies the speed by the twelfth root of two, about 1.05946. For n semitones the ratio is 2^(n/12). Going the other way, semitones = 12 × log2(ratio). A ratio of 2 is twelve semitones up, one octave, and a ratio of 0.5 is an octave down. Length is divided by the ratio, and a tempo is multiplied by it.

A worked example

Start with a pitch shift of +3 semitones. The ratio is 1.1892, so the sample plays at 118.9207 percent of its original speed. A 4-second sample becomes 3.3636 seconds long, and a 100 BPM loop becomes 118.9207 BPM. To get the same length back without the pitch change you would need to time-stretch by a factor of 0.8409, which is 1 divided by the ratio. Start instead from a tempo change of 100 to 120 BPM and the ratio is 1.2, which is 3.16 semitones, so speeding up a drum loop to match a track also moves it up a little over three semitones.

Three starting points

A pitch shift is the direct way: type the number of semitones, negative for down, from -48 to 48. A tempo change asks for the original and the target tempo and tells you how many semitones the pitch will move if you simply speed the sample up, which is why sampled loops are often matched by a time-stretch instead. A sample-rate mismatch handles a common error: a file recorded at one rate and played at another. A file at 44,100 Hz played at 48,000 Hz runs 8.84 percent fast and sounds about 1.47 semitones sharp.

Varispeed and time-stretching

Varispeed changes pitch and length together. A time-stretch algorithm changes one without the other, by cutting the audio into small pieces and overlapping them, as the Audio Speed Changer does. Each approach has artefacts. Varispeed sounds natural for moderate changes but alters the character of voices; stretching can add a slight smearing of transients. The page tells you the stretch that would hold the pitch constant, so you can choose.

Practical uses

Match a sample to a song in another key by shifting it the number of semitones between the keys. Slow a recording down by 12 semitones to hear a fast passage an octave lower, the old trick for working out a solo by ear. Check how far a tape-speed error shifted a recording. Calculate what a pitch-up control on a record deck does to a track’s tempo.

Edge cases

The formula is exact, but real devices round: a sampler may offer steps of a cent, or a turntable a percentage. A whole-percent pitch fader gives uneven semitone steps, since 8 percent is 1.33 semitones and not a neat number. For very large changes, high-frequency content can leave the audible band or alias.

Limits

It performs arithmetic and does not process audio. It cannot estimate formant shift. Values are shown to four decimal places.

Related tools

• Audio Speed Changer changes speed and can keep the pitch.
• Delay Time Calculator turns tempo into note lengths.
• Tap Tempo measures the tempo to match.
• Note Frequency Chart shows the frequency of each semitone.