/**
 * Iterative radix-2 Cooley-Tukey FFT for power-of-two sizes.
 * Used for the fbank computation; not a general-purpose FFT.
 */
/**
 * Forward FFT in-place on (re, im). `size` must be a power of two; re.length === im.length === size.
 */
export declare function fftInPlace(re: Float64Array, im: Float64Array, size: number): void;
/**
 * Real-input FFT. Returns the first `size/2 + 1` complex bins as two arrays.
 * Allocates internal buffers of length `size`. Treats input as real (imag=0).
 */
export declare function rfft(input: Float64Array, size: number): {
    re: Float64Array;
    im: Float64Array;
};
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