How Speed and Pitch Relate in Digital Resampling
In physics and digital signal processing, frequency is directly proportional to playback rate. When an audio buffer is played back faster, sound waves arrive at your ears with higher frequency (higher musical pitch). When played back slower, sound waves stretch out, lowering the fundamental pitch and harmonics.
Mathematically, the relationship is logarithmic:
For example, setting playback speed to 0.50x (half-speed) drops the pitch by exactly -12 semitones (one full octave). Setting speed to 0.84x drops the pitch by roughly -3 semitones.
Speed to Semitone Conversion Reference Table
| Speed Setting | Approximate Semitone Shift | Aesthetic Character | Common Genre Usage |
|---|---|---|---|
| 0.50x | -12.0 semitones (-1 octave) | Ultra Slow, subterranean bass | Ambient drone, experimental lo-fi |
| 0.75x | -5.0 semitones | Heavy chopped tempo, deep baritone | Houston chopped & screwed |
| 0.84x | -3.0 semitones | Relaxed dreamy mood, soulful vocals | Classic Slowed + Reverb |
| 1.00x | 0.0 semitones | Original tempo and key | Standard playback |
| 1.12x | +2.0 semitones | Upbeat tempo, bright vocal lift | Sped-up pop edits, workout playlists |
| 1.20x | +3.2 semitones | High energy, signature anime vocal key | Classic Nightcore |
Why Resampling Sounds Better Than Phase Vocoders
Many online speed changers advertise "change speed without changing pitch." While useful for transcribing spoken podcasts, synthetic phase vocoders split audio into short overlapping time slices (FFT grains) and reconstruct them.
This process routinely creates phase smear, dulls transient percussion, and introduces an unpleasant metallic warble in cymbals and vocals. Resampling, in contrast, changes speed and pitch together without touching phase coherence, ensuring maximum analog warmth and pristine audio quality.
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Sound Principles & Technical References
- W3C Web Audio API: playbackRate Parameter — Specification for smooth k-rate and a-rate audio resampling.
- Acoustics of Musical Intervals — Logarithmic relationships between frequency ratios and musical semitone divisions.
- Phase Vocoder Theory & Artifacts — The technical tradeoffs between granular time-stretching and time-domain resampling.
Frequently Asked Questions
Does changing audio speed also change the pitch?
Yes, when using resampling (the technique SoundWell uses). Slowing down an audio track lowers the pitch, while speeding it up raises the pitch, identically to tape machines or vinyl records. This maintains natural acoustic timbre without the robotic artifacts caused by time-stretching.
Can I change speed and pitch independently?
SoundWell intentionally uses coupled speed and pitch resampling because it delivers the purest, warmest sound for lo-fi, slowed + reverb, and nightcore genres. Independent time-stretching often introduces phase smearing and metallic distortion.
What is the speed range supported in SoundWell?
SoundWell supports playback rates from 0.50x (half-speed, exactly one octave down) up to 1.20x (20% faster, approximately 3 semitones up into nightcore range) with 0.01x precision.
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