Descending Sine Wave ? -Sound Forge - PC - MAGIX Community Forums Archive

Subject:Descending Sine Wave ? Posted by: PixelStuff Date:8/5/2002 1:59:19 PM Hey, Is there a way in Sound Forge to create a descending sine wave which goes from exactly 300Hz down to 20Hz in 60 or maybe 90 seconds? I played with creating a simple sine wave and then using pitch bend to lower the frequencey but there doesn't seem to be any way of knowing exactly how much it is changing. And pitch bend seems to max out before the signal gets very low. Any suggestions? JBJones
Subject:RE: Descending Sine Wave ? Reply by: Chienworks Date:8/5/2002 2:21:33 PM The center frequency between 300 and 20Hz is 77.46Hz. The octave spread from the center to either end frequency is 1.953 octaves, which is 23.44 semitones. So if you synthesize a 77.46Hz sinewave, then set the pitch bend to go from +23.5 semitones down to -23.5 semitones you'll be very close. I just tried this with a 60 second file and the resulting length was about 44.87 seconds, so starting with 80.23 seconds (which can't be done in a single piece because the maximum synthesis length is 60) will result in about a 60 second file. The biggest inaccuracy will come from the fact that you can't select precise points in the pitch bend screen with the mouse. Explanations of the math: To calculate the center frequency (cf) from the upper and lower frequencies (uf, lf), multiply uf x lf and take the square root. The octaves from one frequency to another = (log (uf / cf)) / log 2 Semitones are equal to octaves x 12

The center frequency between 300 and 20Hz is 77.46Hz. The octave spread from the center to either end frequency is 1.953 octaves, which is 23.44 semitones. So if you synthesize a 77.46Hz sinewave, then set the pitch bend to go from +23.5 semitones down to -23.5 semitones you'll be very close. I just tried this with a 60 second file and the resulting length was about 44.87 seconds, so starting with 80.23 seconds (which can't be done in a single piece because the maximum synthesis length is 60) will result in about a 60 second file. The biggest inaccuracy will come from the fact that you can't select precise points in the pitch bend screen with the mouse.

Explanations of the math:

To calculate the center frequency (cf) from the upper and lower frequencies (uf, lf), multiply uf x lf and take the square root.

The octaves from one frequency to another = (log (uf / cf)) / log 2

Semitones are equal to octaves x 12