I have written blog posts about audio measurements, trying to explain what do they tell us and what should be known when interpreting the results. These are no comprehensive instructions or explanations but brief notes on the most important points of these measurements.
According to Audio Precision, there are six basic audio measurements, also presented in AP Technote 104:
- Frequency response
- Signal-to-Noise Ratio
In a modern high quality audio device, level, frequency response, and phase are more like sanity checks than actual performance measurements – at least within audio band. Level should be as per chosen by the designer or set by user, frequency response should be flat in the audio band, and phase should show no surprises either. While these are important to check, the focus is often on the rest of the measurements.
Expresses “leaking” between channels; it is measured by driving a stimulus signal in one channel while listening the other. Crosstalk is expressed as a ratio between the quiet undriven channel and the stimulus in the driven channel, and given in decibels. In stereo system, crosstalk is measured by driving a stimulus signal in one channel while listening the other. As the signal level is very small, sharp bandpass filter is … Continue reading
Presents the unwanted part of the signal – something that was not put there and should not be there. THD+N vs. amplitude graph is important as it reveals SNR, dynamic range, and THD+N ratio; all are expressed as ratio compared to a specified signal level. Signal level, signal frequency, and measurement bandwidth must be known (or guessed) when analysing results. THD+N, Total Harmonic Distortion plus Noise, is one of the best audio … Continue reading
SNR is a ratio of level measurement and noise measurement (both typically as RMS level), expressed in dB. Signal level, measurement bandwidth, and weighting filter must be defined. Dynamic range is like SNR but noise is measured in the presence of small signal; results should be the same. Noise is one of the most important performance figures and typically compared to the signal level as SNR, Signal-to-Noise Ratio. In audio … Continue reading