Comparing Audio Noise Results with Matched Weighting and Bandwidth

Two audio noise numbers can differ even when the underlying waveform is unchanged. Weighting filters and measurement bandwidth determine which spectral components contribute to the reported result. Match those settings before using a lower number as evidence that an amplifier, DAC, or board became quieter.

Record the complete noise definition

The TI PCM512x data sheet specifies filter conditions with its audio measurements, including A weighting for signal to noise and dynamic range results. Such conditions are part of the specification, rather than optional footnotes.

Record high pass and low pass filters, weighting curve, detector or RMS method, integration time, and voltage reference. Keep electrical dBV or dBFS separate from acoustic sound pressure measurements; the same weighting name does not make their references interchangeable.

Keep the circuit state consistent

Document gain, load, source termination, digital input pattern, and mute state. A noise measurement with an internally muted output may not represent the noise during quiet passages of active playback.

For an input amplifier, reproduce the intended source impedance or a clearly defined test termination. An open input can pick up interference and generate a result unrelated to the specified source condition. A shorted input answers a different question from one connected to a noisy source.

Retain the spectrum as supporting evidence

Measure the integrated value and inspect a spectrum covering the useful band. Separate narrow hum or clock related tones from broadband noise. A weighting filter can reduce the contribution of some components without removing them from the physical output.

Do not apply a fixed numerical offset to convert every unweighted result into an A weighted result. The difference depends on the distribution of noise over frequency. A spectrum dominated by low frequency hum behaves differently from one dominated by a midband tone.

Check the measurement floor

Characterize the analyzer with the same input range and a suitable termination. Verify that the device noise is sufficiently above the instrument contribution for the intended comparison. Reducing range can improve sensitivity but may also expose the input to clipping from an unexpected signal or DC component.

Repeat the baseline after changing cables or grounding. Keep the voltage measured at the device and the analyzer’s input configuration together so a connection change is not mistaken for a component improvement.

Save weighted and unweighted results when both help diagnose the design, clearly labeling each. Include the spectrum and operating state with the acceptance result. A meaningful comparison uses the same measurement definition and explains which noise components changed. A more favorable number produced solely by changing filters is a reporting change, not evidence of a quieter circuit.