posted 23 January 2001 07:34            

spl40.txt

One uses a swept oscillator, the other uses a swept pink noise source through a constant 20% fractional width bandpass filter.

Both of these sources are swept logarithmically in frequency, and the output goes through an attenuator that is driven by a lockstep (in frequency) Fletcher-Munson loudness correction corresponding to moderate listening levels of 40 dBSPL.

Kyma has trouble pasting large clipboard cuttings, so if you attempt to run the included program to regenerate the Fletcher-Munson correction table, you will have to cut and paste in 1000 line pieces. But the correction table is also included here as an AIF file.

posted 23 January 2001 23:27            

const-loudness.kym 2decade_exp.aif

1. I created a 2-decade exponentail sweep to ensure that I sweep from 100 Hz to 10 KHz. The previous exponential sweep was some arbitrary version from the Kyma library.

2. I smooth the choke VCA for click prevention when the sweep retraces.

3. There is a threshold setting for extracting only that portion of the Fletcher-Munson curve below the threshold. This allows one to have greater loudness amplitude at the expense of a slight reduction in the audible portion of the sweep range. This is used to boost output gain as well as to choke off frequencies that would lie above the threshold.