snr - Signal to noise and edr - effective decay ranges

The signal-to-noise-range (snr) and the effective-decay-range (edr) are important parameters providing information about the quality of the measurement and parameter calculations. For the default settings they are always the first parameters given in the results table as shown below.

They are not included in the Calculate->User Defined->Settings… dialog, but will also be calculated and displayed if Calculate->User Defined->Settings… is selected.

The edr can also be displayed as marks above each value in the room acoustics plots as shown below.

The actual signal to noise ratio of an impulse response measurement is estimated from the resulting response itself, and presented as the snr. The estimation of the background noise level is done using the last 10% of the impulse response, and the accuracy thereby depends on that the last 10 % of the impulse response is actually being a flat noise floor. This snr number is, however, not of much practical use in room acoustical analysis.

Of much more interest is the so-called effective decay range, edr, which directly describes the range of the decay curve which is available for analysis. For an explanation of the decay curve, see the  Advanced Calculation Options section.

The effective decay range is taken as the level of the decay curve at the point where the response is truncated before forming the decay curve. The resulting decay range is therefore, in addition to the physical signal-to-noise ratio in the measurement, dependent on the type and shape of the room impulse response and the chosen noise margin in the response truncation.

The decay range can be used directly to evaluate the quality of the room acoustical parameter calculations, especially the reverberation time T30. It should be noted, and is illustrated clearly in the examples in the More theory about integration section, that if no compensation for energy removed by truncation has been done, the decay range as calculated here is meaningless. It will therefore not be displayed in the results grid unless both truncation and compensation are checked in  Advanced Calculation Options.

If you are evaluating a room acoustics parameter that requires two impulse responses, e.g. IACC or LF, two rows of snr and edr will appear in the table, one row for each impulse response.