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librosa.filters._multirate_fb¶

librosa.filters._multirate_fb(center_freqs=None, sample_rates=None, Q=25.0, passband_ripple=1, stopband_attenuation=50, ftype='ellip', flayout='sos')[source]¶

Helper function to construct a multirate filterbank.

A filter bank consists of multiple band-pass filters which divide the input signal into subbands. In the case of a multirate filter bank, the band-pass filters operate with resampled versions of the input signal, e.g. to keep the length of a filter constant while shifting its center frequency.

This implementation uses scipy.signal.iirdesign to design the filters.

Parameters

center_freqsnp.ndarray [shape=(n,), dtype=float]

Center frequencies of the filter kernels. Also defines the number of filters in the filterbank.

sample_ratesnp.ndarray [shape=(n,), dtype=float]

Samplerate for each filter (used for multirate filterbank).

Qfloat

Q factor (influences the filter bandwith).

passband_ripplefloat

The maximum loss in the passband (dB) See scipy.signal.iirdesign for details.

stopband_attenuationfloat

The minimum attenuation in the stopband (dB) See scipy.signal.iirdesign for details.

ftypestr

The type of IIR filter to design See scipy.signal.iirdesign for details.

flayoutstring

Valid output argument for scipy.signal.iirdesign.

If ba, returns numerators/denominators of the transfer functions, used for filtering with scipy.signal.filtfilt. Can be unstable for high-order filters.
If sos, returns a series of second-order filters, used for filtering with scipy.signal.sosfiltfilt. Minimizes numerical precision errors for high-order filters, but is slower.
If zpk, returns zeros, poles, and system gains of the transfer functions.

Returns

filterbanklist [shape=(n,), dtype=float]: Each list entry comprises the filter coefficients for a single filter.
sample_ratesnp.ndarray [shape=(n,), dtype=float]: Samplerate for each filter.

Raises

ParameterError: If center_freqs is None. If sample_rates is None. If center_freqs.shape does not match sample_rates.shape.