/**
 * Frequency-to-time reconstruction: alias reduction, IMDCT, and the synthesis
 * polyphase filterbank.
 *
 * Layer III encodes in two nested transforms. A 32-band polyphase filterbank
 * splits the signal into sub-bands, then an MDCT gives each sub-band 18 finer
 * frequency lines. Decoding runs both in reverse, and three corrections are
 * needed along the way:
 *
 * - **Alias reduction** undoes the overlap between neighbouring polyphase bands.
 *   The filterbank is not perfectly band-limited, so each band leaks into its
 *   neighbours; eight butterflies across every boundary cancel it. Skipped for
 *   short blocks, where the encoder does not apply the matching step.
 * - **Overlap-add** stitches successive IMDCT outputs together. Each transform
 *   produces 36 samples for 18 new ones; the second half is carried into the
 *   next granule. This is what makes the transform critically sampled.
 * - **Frequency inversion** negates alternate samples in odd sub-bands, undoing
 *   the modulation the analysis filterbank applied.
 */
import type { GranuleInfo } from './sideinfo.js';
/**
 * Cancels aliasing between adjacent sub-bands.
 *
 * Operates on the boundary between each pair of the 32 sub-bands, mixing the
 * last 8 lines of one with the first 8 of the next.
 */
export declare function reduceAlias(spectrum: Float32Array, granule: GranuleInfo): void;
/**
 * Inverse MDCT with windowing and overlap-add.
 *
 * @param spectrum 576 requantized lines, sub-band major.
 * @param overlap 576 carried-over samples from the previous granule, updated in place.
 * @param out 576 time-domain samples, sub-band major (18 per sub-band).
 */
export declare function imdct(spectrum: Float32Array, granule: GranuleInfo, overlap: Float32Array, out: Float32Array): void;
/**
 * Negates every other sample in odd sub-bands.
 *
 * The analysis filterbank modulates alternate bands; this undoes it. Omitting it
 * produces audio that is recognisable but harsh, because half the sub-bands come
 * out phase-inverted.
 */
export declare function invertFrequency(samples: Float32Array): void;
/**
 * The synthesis polyphase filterbank.
 *
 * Turns 32 sub-band samples into 32 PCM samples, using a 1024-sample history so
 * the reconstruction filter has the past it needs. One instance per channel —
 * the history is stateful and must not be shared.
 */
export declare class SynthesisFilterbank {
    #private;
    /** Discards history, e.g. after a seek. */
    reset(): void;
    /**
     * Produces 32 PCM samples from 32 sub-band samples.
     *
     * @param subbands 32 sub-band values for one time slot.
     * @param out Destination for 32 PCM samples.
     * @param outOffset Where to write in `out`.
     */
    process(subbands: Float32Array, out: Float32Array, outOffset: number): void;
}