File nprmeas_core.h¶

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NPRMeasure — notched-noise Noise Power Ratio. More...

• #include "clib_common.h"
• #include "jm_perf.h"
• #include "measure/measure_core.h"
• #include "psd/psd_core.h"
• #include <complex.h>

Classes¶

Public Functions¶

Detailed Description¶

Drive the system with band-limited noise containing a deep notch; NPR is the ratio of the mean in-band noise PSD to the mean PSD that folds into the notch (distortion + quantisation + intermodulation). The band/notch geometry is an analyze() argument, so one estimator can sweep several notch placements.

Lifecycle: create -> [analyze]* -> destroy

Public Functions Documentation¶

function nprmeas_analyze¶

NPR of a notched-noise capture.

npr_meas_t nprmeas_analyze (
    nprmeas_state_t * state,
    const float * x,
    size_t n_in,
    double active_lo,
    double active_hi,
    double notch_lo,
    double notch_hi,
    double guard_hz
) 

Parameters:

• state The analyser.
• x Real time-domain capture.
• n_in Number of input samples.
• active_lo Active noise band lower edge (Hz).
• active_hi Active noise band upper edge (Hz).
• notch_lo Notch lower edge (Hz).
• notch_hi Notch upper edge (Hz).
• guard_hz Keep-out around the notch edges (Hz).

Returns:

the NPR metric record (by value).

>>> from doppler.measure import NPRMeasure
>>> import numpy as np
>>> rng = np.random.default_rng(0)
>>> n = 1 << 15
>>> F = np.fft.rfft(rng.standard_normal(n))
>>> f = np.fft.rfftfreq(n)
>>> F[(f < 0.05) | (f > 0.45)] = 0                 # band-limit to [0.05,0.45]
>>> F[(f >= 0.20) & (f <= 0.25)] *= 10**(-50/20)   # notch 50 dB deep
>>> x = np.fft.irfft(F, n)
>>> x = (0.3*x/np.std(x)).astype(np.float32)
>>> r = NPRMeasure(n=n, fs=1.0).analyze(x, 0.05, 0.45, 0.20, 0.25, 0.01)
>>> 45 < r.npr_db < 55, r.notch_psd_dbfs < r.inband_psd_dbfs
(True, True)

function nprmeas_create¶

Create an NPRMeasure analyser (auto Kaiser window).

nprmeas_state_t * nprmeas_create (
    size_t n,
    double fs,
    double full_scale,
    size_t bits,
    double dynamic_range_db
) 

The window is always Kaiser; its shape is auto-selected so the sidelobes sit below the requested dynamic range (see measure_resolve_dr()). The chosen window also sets a minimum notch keep-out so active-band noise cannot leak into the notch average through the window skirt.

Parameters:

• n Capture/frame length (>= 2).
• fs Sample rate (Hz, > 0).
• full_scale Amplitude that equals 0 dBFS (> 0). Ignored if bits > 0.
• bits ADC depth: bits>0 sets the 0-dBFS reference to 2^(bits-1) and, unless overridden, the dynamic-range target.
• dynamic_range_db Explicit sidelobe/dynamic-range target (dB); used when > 0, else derived from bits.

Returns:

Heap state, or NULL on bad args / allocation failure.

function nprmeas_destroy¶

Destroy an NPRMeasure analyser.

void nprmeas_destroy (
    nprmeas_state_t * state
) 

Parameters:

• state May be NULL.

function nprmeas_reset¶

Reset (no-op: each analyze() call is independent).

void nprmeas_reset (
    nprmeas_state_t * state
) 

function nprmeas_spectrum_dbfs¶

DC-centred dBFS magnitude spectrum of a capture (length nfft). The same averaged PSD the metrics use, for an analyzer-display backdrop.

size_t nprmeas_spectrum_dbfs (
    nprmeas_state_t * state,
    const float * x,
    size_t x_len,
    float * out
) 

function nprmeas_spectrum_dbfs_max_out¶

Capacity (== nfft) of the spectrum_dbfs output buffer.

size_t nprmeas_spectrum_dbfs_max_out (
    nprmeas_state_t * state
) 

The documentation for this class was generated from the following file native/inc/nprmeas/nprmeas_core.h