Class dft_resampler¶

`class` dft_resampler<T> dft ¶

template <typename T>
class dft_resampler { … }

FFT-based sample-rate converter and FIR filter using overlap-save.

Performs power-of-two resampling (upsampling, downsampling, or filter-only when the factor is 1) of a real-valued signal. The lowpass anti-aliasing / anti-imaging filter is a Kaiser-windowed sinc designed from the requested stopband attenuation and transition width, pre-transformed into the frequency domain so that each frame only requires a forward real FFT, spectral shaping (gain multiplication and stopband zeroing, plus conjugate mirroring / truncation for up/downsampling), and an inverse real FFT.

Template parameters
T	Sample type ( `float` or `double` ).

`function` kaiser_beta_from_attenuation(T) ¶

static T kaiser_beta_from_attenuation(T att)

Computes the Kaiser window beta from a desired stopband attenuation.

Parameters
att	Desired stopband attenuation in dB.

Returns
	Kaiser beta parameter.

Fully qualified name: kfr::dft_resampler<T>::kaiser_beta_from_attenuation(T)

Declared at dft/dft_resampler.hpp:153

`function` input_block_size() ¶

size_t input_block_size() const noexcept

Returns the input FFT block size \(N\) .

Fully qualified name: kfr::dft_resampler<T>::input_block_size()

Declared at dft/dft_resampler.hpp:163

`function` factor() ¶

size_t factor() const noexcept

Returns the resampling factor (a power of two, >= 1).

Fully qualified name: kfr::dft_resampler<T>::factor()

Declared at dft/dft_resampler.hpp:165

`function` is_downsampling() ¶

bool is_downsampling() const noexcept

Returns true if this resampler downsamples by factor() .

Fully qualified name: kfr::dft_resampler<T>::is_downsampling()

Declared at dft/dft_resampler.hpp:167

`function` filter_length() ¶

size_t filter_length() const noexcept

Returns the designed filter length (in filter-rate samples).

Fully qualified name: kfr::dft_resampler<T>::filter_length()

Declared at dft/dft_resampler.hpp:169

`function` output_block_size() ¶

size_t output_block_size() const noexcept

Returns the output FFT block size \(M\) .

Fully qualified name: kfr::dft_resampler<T>::output_block_size()

Declared at dft/dft_resampler.hpp:171

`function` input_hop() ¶

size_t input_hop() const noexcept

Returns the number of new input samples consumed per frame.

Fully qualified name: kfr::dft_resampler<T>::input_hop()

Declared at dft/dft_resampler.hpp:173

`function` output_hop() ¶

size_t output_hop() const noexcept

Returns the number of valid output samples produced per frame.

Fully qualified name: kfr::dft_resampler<T>::output_hop()

Declared at dft/dft_resampler.hpp:175

`function` reset() ¶

void reset() noexcept

Resets the resampler to its freshly-constructed state, clearing all buffered input without changing filter parameters.

Fully qualified name: kfr::dft_resampler<T>::reset()

Declared at dft/dft_resampler.hpp:181

`function` compute_block_size(size_t, T, T) ¶

static size_t compute_block_size(size_t upsample_factor, T stopband_atten_db, T transition_width)

Computes the minimal power-of-two block size required for the given filter parameters (Kaiser formula).

Parameters
upsample_factor	The upsampling factor used in the transition-width scaling.
stopband_atten_db	Desired stopband attenuation in dB.
transition_width	Transition bandwidth normalised to the lower-rate Nyquist (0..1).

Returns
	The computed block size (a power of two).

Fully qualified name: kfr::dft_resampler<T>::compute_block_size(size_t, T, T)

Declared at dft/dft_resampler.hpp:196

`constructor` dft_resampler<T>(const dft_resampler_params &) ¶

explicit dft_resampler(const dft_resampler_params& params)

Constructs the resampler from the given parameters.

Parameters
params	Resampler parameters.

Fully qualified name: kfr::dft_resampler<T>::dft_resampler<T>(const dft_resampler_params &)

Declared at dft/dft_resampler.hpp:218

`function` process_frame(const T *) ¶

T* process_frame(const T* input)

Processes one frame in-place and returns a pointer to the valid output.

Parameters
input	Pointer to `input_block_size()` input samples.

Returns
	Pointer to `output_hop()` valid (un-normalised) output samples.

Fully qualified name: kfr::dft_resampler<T>::process_frame(const T *)

Declared at dft/dft_resampler.hpp:377

`function` process_frame(T , const T ) ¶

void process_frame(T* output, const T* input)

Processes one frame via overlap-save and writes normalised output.

Parameters
output	Output buffer of at least `output_hop()` samples.
input	Pointer to `input_block_size()` input samples.

Fully qualified name: kfr::dft_resampler<T>::process_frame(T *, const T *)

Declared at dft/dft_resampler.hpp:438

`function` process(std::span<T>, std::span<const T>) ¶

size_t process(std::span<T> output, std::span<const T> input)

Processes an arbitrary-length input stream and writes the resampled output.

Parameters
output	Output buffer. Must be large enough to hold all frames produced (a logic check is performed per frame).
input	Input samples (any size).

Returns
	Number of output samples actually written.

Fully qualified name: kfr::dft_resampler<T>::process(std::span<T>, std::span<const T>)

Declared at dft/dft_resampler.hpp:458

Fully qualified name: kfr::dft_resampler<T>

Declared at dft/dft_resampler.hpp:120

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Class dft_resampler¶