Decay range (SNR)

The signal-to-noise ratio (SNR) is not included in the Parameter Settings dialog, it is however an important parameter, and for the default settings it is always the first parameter given in the results grid and can be displayed as marks in the room acoustics plots. It is therefore discussed here.

Utilizing the phase randomizing property of the MLS deconvolution, the actual signal to noise ratio in the impulse response measurement can be estimated from the resulting response itself. This ratio is, however, not of much practical use in room acoustical analysis. Of much more interest is the so-called decay range, which directly describes the range of the decay curve which is available for analysis. For an explanation of the decay curve, see the Integration options section.

The SNR in dB as displayed by WinMLS is actually the decay range. It 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 Integration options 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 Truncation and compensation is chosen in Room Acoustics->Calculation Options->Integration Options.

If a secondary impulse response is used due to the chosen microphone option, a second row of SNRs will appear in the result grid. This is calculated separately for the secondary response.