dspark::StretchedSincReader< T > Class Template Reference

Band-limited fractional reader for read rates from 1 to 4. More...

#include <Interpolation.h>

Public Member Functions
	StretchedSincReader ()
	Builds the kernel tables (allocates: construct on a setup thread).
T	readRing (const T *ring, int64_t mask, int64_t intPos, double frac, int step) const noexcept
	Reads a power-of-two ring buffer at intPos + frac with the kernel of a rate step. It needs the samples intPos - reach(step) + 1 through intPos + reach(step).
int	reach (int step) const noexcept

Static Public Member Functions
static int	stepFor (double rate) noexcept
	The table for a read rate: the nearest tabulated rate at or above it. Costs a log2, so look it up once per constant rate.

Static Public Attributes
static constexpr int	kSteps = 16
	Tabulated rates.
static constexpr int	kStepsPerOctave = 8
	Rate resolution.
static constexpr int	kPhases = 64
	Phases per rate.
static constexpr int	kMaxTaps = 128
	Kernel length at rate 4.

Detailed Description

template<FloatType T>
class dspark::StretchedSincReader< T >

Band-limited fractional reader for read rates from 1 to 4.

A read point that advances by r > 1 samples per output sample decimates: content above Nyquist / r folds back unless the kernel's cutoff drops to Nyquist / r. This reader tabulates such kernels (the sinc stretched by r under a Kaiser window, beta 10, about 32 r taps) for 16 rates in eighth-octave steps from 2^(1/8) to 4, at 64 phases each, and reads with the kernel of the nearest tabulated rate at or above the requested one: nothing folds back from beyond the output Nyquist, and the band gives up at most an eighth of an octave at the top. Passband error stays below -76 dB up to three quarters of the cutoff. For rates at or below 1 use SincInterpolator.

Threading: the constructor builds about 60 k coefficients (allocates: setup thread); reads are const, allocation-free and safe from any thread.

Template Parameters

T	Sample type (float or double).

Definition at line 446 of file Interpolation.h.

Constructor & Destructor Documentation

StretchedSincReader()

template<FloatType T>

dspark::StretchedSincReader< T >::StretchedSincReader ( )

inline

Builds the kernel tables (allocates: construct on a setup thread).

Definition at line 455 of file Interpolation.h.

Member Function Documentation

reach()

template<FloatType T>

int dspark::StretchedSincReader< T >::reach ( int  step ) const

inlinenoexcept

Returns

Samples a read of this step reaches on either side of intPos.

Definition at line 552 of file Interpolation.h.

readRing()

template<FloatType T>

T dspark::StretchedSincReader< T >::readRing ( const T *  ring, int64_t  mask, int64_t  intPos, double  frac, int  step  ) const

inlinenoexcept

Reads a power-of-two ring buffer at intPos + frac with the kernel of a rate step. It needs the samples intPos - reach(step) + 1 through intPos + reach(step).

Parameters

ring	Ring storage.
mask	Ring size minus one (the size must be a power of two).
intPos	Integer read position (masked, so any value works).
frac	Fractional position in [0, 1).
step	Rate step from stepFor().

Returns

Interpolated value.

Definition at line 522 of file Interpolation.h.

stepFor()

template<FloatType T>

static int dspark::StretchedSincReader< T >::stepFor ( double  rate )

inlinestaticnoexcept

The table for a read rate: the nearest tabulated rate at or above it. Costs a log2, so look it up once per constant rate.

Parameters

rate	Read rate, clamped to [2^(1/8), 4].

Returns

Step index in [0, kSteps).

Definition at line 505 of file Interpolation.h.

Member Data Documentation

kMaxTaps

template<FloatType T>

constexpr int dspark::StretchedSincReader< T >::kMaxTaps = 128

staticconstexpr

Kernel length at rate 4.

Definition at line 452 of file Interpolation.h.

kPhases

template<FloatType T>

constexpr int dspark::StretchedSincReader< T >::kPhases = 64

staticconstexpr

Phases per rate.

Definition at line 451 of file Interpolation.h.

kSteps

template<FloatType T>

constexpr int dspark::StretchedSincReader< T >::kSteps = 16

staticconstexpr

Tabulated rates.

Definition at line 449 of file Interpolation.h.

kStepsPerOctave

template<FloatType T>

constexpr int dspark::StretchedSincReader< T >::kStepsPerOctave = 8

staticconstexpr

Rate resolution.

Definition at line 450 of file Interpolation.h.

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The documentation for this class was generated from the following file:

• Interpolation.h