Stationary Loudness Calculations Don´t Match Expected Outputs

Updated Apr 3, 2018

Reported In

Software

  • LabVIEW Sound and Vibration Toolkit

Issue Details

I´m testing the Stationary Loundness VI using the Stationary Loudness and Sharpness (Simulated) Example. If I input a 1kHz pure tone (no modulation) at 40dB I should output 1 Sones and 40 Phons. However I´m receiving  0,937 Sones and 39,1 Phons.

The output values doesn´t match the expected values. What is wrong?

Solution

Sound Quality standards were written assuming that a 'perfect' tone would have -20 dBc sidebands. With the precision of the 1/3 octave filters, we have to add these sideband signal components when simulating the test signal. With sideband energy added, the measured loudness is 0.977 Sones, and this is within the expected tolerance for a stationary loudness measurement.

Additional Information

The phon is a unit of loudness level for pure tones. Its purpose is to compensate for the effect of frequency on the perceived loudness of tones. By definition, the number of phon of a sound is the dB SPL of a sound at a frequency of 1 kHz that sounds just as loud. This implies that 0 phon is the limit of perception, and inaudible sounds have negative phon levels.

The sone is a unit of loudness, how loud a sound is perceived. The sone scale is linear. Doubling the perceived loudness doubles the sone value.

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