The MSP phasor~ object is frequently used as a low-frequency control signal for audio. Because it is often used to control other signals over a specific period of time, phasor~ can use tempo-relative timing, too. The frequency (rate) of a phasor~ is normally specified in Hertz, but you can alternatively give phasor~ a time interval, using tempo-relative time units, and it will use the inverse of that to determine its frequency.
This patch enables you to pan a sound to any azimuth angle in a quadraphonic sound system. The abstraction assumes a square configuration of four equidistant speakers: 1 = front left, 2 = front right, 3 = rear left, 4 = rear right. The sound signal comes in the left inlet, and the azimuth angle comes in the right inlet, either as a number or as a signal.
This shows an implementation of phase distortion synthesis in MSP—using the phasor~, kink~, and cycle~ objects—in a patch that is designed to be used inside the poly~ object. For an explanation of this sort of phase distortion synthesis, see “A demonstration of phase distortion synthesis.” The main point of this example, though, is to show how a synthesis patch can be designed to respond directly to MIDI input.
In "Constant power panning using square root of intensity" we used the square root of the desired intensity for each speaker to calculate the amplitude of each speaker. However, square root calculations are somewhat computationally intensive, and it would be nice if we could somehow avoid having to perform two such calculations for every single audio sample. As it happens, the sum of the squares of sine and cosine functions also equals 1.
This pan~ subpatch takes one signal in the left inlet, and sends it out each of two outlets. The amplitude gain for each outlet is determined by a panning value supplied in the right inlet. This value can be supplied as a typed-in argument in the main patch, as a float value, or as a control signal.
If you want to change the coefficients of biquad~ in real time while a sound is playing, it's usually better to use MSP signals rather than individual Max messages, to avoid causing clicks. In that case, you should replace filtergraph~ with filtercoeff~ and send the frequency, gain, and Q parameters into filtercoeff~ as smooth signals (as shown in the left portion of the example).
This example demonstrates one of MSP's many filter objects—the resonant bandpass filter reson~—and demonstrates how a parameter of that filter—in this case its center frequency—can be easily modulated by a low-frequency control oscillator (cycle~). The range of cycle~ is between 1 and -1, but that range can be amplified by multiplication, and can be offset by addition.
For linear interpolation of a MSP signal, the line~ object sends out a signal that progress to some new value over a certain amount of time interpolating sample-by-sample along the way. The input to line~ is a pair of numbers representing a destination value (where it should eventually arrive) and a transition time (how long it should take to get there). It can receive multiple pairs of numbers in a single message, and it will use the pairs in order, starting each new pair when the previous transition has finished.