/**
 * Tempo and pitch manipulation.
 *
 * Two distinct operations that are easy to confuse:
 *
 * - **`changeSpeed`** resamples. Playing a record faster raises its pitch; this
 *   does the digital equivalent. Cheap, and correct when you want the
 *   "chipmunk" behaviour.
 * - **`changeTempo`** uses WSOLA (Waveform Similarity Overlap-Add) to change
 *   duration while holding pitch constant — a podcast at 1.5× that still sounds
 *   like the same person.
 *
 * WSOLA works by cutting the signal into overlapping windows and reassembling
 * them at a different spacing. The "waveform similarity" part is what makes it
 * usable: naively overlapping windows at arbitrary offsets causes phase
 * cancellation that sounds like flanging or echo, so each window is nudged
 * within a small search range to the position where it best correlates with the
 * natural continuation of the previous one.
 */
/**
 * Changes playback speed, altering pitch with it.
 *
 * @param factor `2` plays twice as fast and an octave higher; `0.5` halves both.
 */
export declare function changeSpeed(channels: readonly Float32Array[], factor: number): Float32Array[];
/**
 * Changes duration while preserving pitch.
 *
 * @param factor `1.5` makes it 1.5× faster (shorter); `0.5` makes it twice as long.
 */
export declare function changeTempo(channels: readonly Float32Array[], factor: number, sampleRate: number): Float32Array[];
/**
 * Shifts pitch without changing duration.
 *
 * Implemented as tempo change followed by resampling: stretch the audio, then
 * play the stretched version at a rate that restores the original length. The
 * pitch change survives; the duration change cancels out.
 *
 * @param semitones Positive raises pitch, negative lowers it.
 */
export declare function changePitch(channels: readonly Float32Array[], semitones: number, sampleRate: number): Float32Array[];