electroacoustics.noise_measurements

Noise measurements of audio equipment (AES17-2015 6.4).

The two levels that say how quiet a device is, both measured through the AES17 measurement chain — the standard notch (5.2.8) where a test tone has to be removed, the CCIR-RMS weighting (5.2.7, the ITU-R BS.468-4 curve with the flat -5,63 dB gain that puts unity at 2 kHz) and the 20 Hz to 20 kHz band (5.2.5):

• Dynamic range (6.4.1), the ratio of the maximum output level to the weighted noise-plus-distortion residual left when the device is driven with a 997 Hz sine 60 dB below full scale — what the standard’s own note also calls the signal-to-noise ratio, since it includes every harmonic, inharmonic and noise component.
• Idle channel noise (6.4.2), the weighted output level, relative to full scale, of a device driven with no signal at all.

They share the notch, the weighting and the band with the distortion metrics of phonometry.electroacoustics.distortion, and differ from them in what is being asked: not how much of the output is not the tone, but how much output there is when there should be none.

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dynamic_range

dynamic_range(
    signal: NDArray[np.float64] | list[float],
    fs: float,
    fundamental: float | None = None,
    *,
    notch_q: float = 2.0,
    bandwidth: float | None = 20000.0,
    full_scale: float = 1.0,
    window: str = 'hann',
) -> float

Dynamic range of an audio device (AES17-2015 6.4.1), in dB CCIR-RMS.

The device is driven with a 997 Hz sine 60 dB below full scale; the captured output has its fundamental removed by the standard notch filter (5.2.8), and the residual noise-plus-distortion is weighted by the CCIR-RMS filter (5.2.7) over the AES17 measurement band. The dynamic range is the ratio of the maximum output level (a full-scale sine, 6.2.6) to that weighted residual level:

$$\mathrm{DR}=20{\log }_{10}\left((\text{full\_scale}/\sqrt{2})/V_{\text{residual,CCIR-RMS}}\right)$$

It includes all harmonic, inharmonic and noise components and is also known as the signal-to-noise ratio (6.4.1 note).

Parameters

Name	Description
signal	Captured output of the device under test (1-D), scaled so that full_scale is the digital full-scale peak amplitude.
fs	Sample rate, in Hz.
fundamental	Test frequency, in Hz; None uses the 997 Hz of the standard.
notch_q	Effective notch quality factor (AES17 5.2.8: 1.2..3; default 2.0).
bandwidth	AES17 measurement bandwidth, in Hz (default 20 kHz; None measures the full Nyquist band).
full_scale	Digital full-scale peak amplitude (default 1.0).
window	FFT window used only for fundamental auto-detection.

Returns: The dynamic range, in dB CCIR-RMS (a positive number).

Raises

Exception	When
ValueError	If the inputs are invalid or notch_q is out of range.

idle_channel_noise

idle_channel_noise(
    signal: NDArray[np.float64] | list[float],
    fs: float,
    *,
    bandwidth: float | None = 20000.0,
    full_scale: float = 1.0,
) -> float

Idle channel noise level (AES17-2015 6.4.2), in dBFS CCIR-RMS.

The weighted output of the device when driven with no signal (a short-circuited analogue input or digital zero at the input). The captured idle output is weighted by the CCIR-RMS filter (5.2.7) over the AES17 measurement band and reported relative to full scale:

$$L_{\text{idle}}=20{\log }_{10}\left(V_{\text{idle,CCIR-RMS}}/(\text{full\_scale}/\sqrt{2})\right)$$

Parameters

Name	Description
signal	Captured idle output of the device under test (1-D), scaled so that full_scale is the digital full-scale peak amplitude.
fs	Sample rate, in Hz.
bandwidth	AES17 measurement bandwidth, in Hz (default 20 kHz; None measures the full Nyquist band).
full_scale	Digital full-scale peak amplitude (default 1.0).

Returns: The idle channel noise level, in dBFS CCIR-RMS (a negative number for any real device).

Raises

Exception	When
ValueError	If the inputs are invalid.