Tutorials and Topics - Peabody Computer Music

Tutorial 2Fundamentals:Adjustable oscillatorFade In and Fade OutThe combination of line~ and *~ also helps to avoid the clicks that can occur when theaudio is turned on and off. The 1 and 0 “on” and “off” messages from the toggle are usedto fade the volume up to the desired amplitude, or down to 0, just as the start or stopmessage is sent to dac~. In that way, the sound is faded in and out gently rather thanbeing turned on instantaneously.On and off messages fade audio in or out before starting or stopping the DACJust before turning audio off, the 0 from toggle is sent to the pack object to start a 100 msfade-out of the oscillator’s volume. A delay of 100 ms is also introduced before sendingthe stop message to dac~, in order to let the fade-out occur. Just before turning the audioon, the desired amplitude value is triggered, beginning a fade-in of the volume; the fadeindoes not actually begin, however, until the dac~ is started—immediately after, in thiscase. (In an actual program, the start and stop message boxes might be hidden from view orencapsulated in a subpatch in order to prevent the user from clicking on them directly.)SummaryMultiplying each sample of an audio signal by some number other than 1 changes itsamplitude; therefore the *~ object is effectively an amplifier. A sudden drastic change ofamplitude can cause a click, so a more gradual fade of amplitude—by controlling theamplitude with another signal—is usually advisable. The line segment signal generatorline~ is comparable to the Max object line and is appropriate for providing a linearlychanging value to the signal network. The combination of line~ and *~ can be used tomake an envelope for controlling the over-all amplitude of a signal.66