The idea of “sample and hold” is to capture the amplitude of a signal at a particular instant in time, and hold it constant for a while. In MSP, the sah~ object allows you to do just that.
When sound waves are mixed together, be it mathematically within the computer or physically in the air, they “interfere” with each other.
This example combines seven pre-recorded saxophone sounds, slowly modulating several aspects of their playback to create an ever-changing mix.
An oscillator is an electronic circuit that generates a cyclic (periodically repeating) signal.
This patch shows a simple way to control the balance between two sounds, and also illustrates the relationship between a) mixing two sounds to one location and b) panning one sound to two locations.
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.
Audio delay is achieved by creating a buffer in which the most recent past sound can be stored. Usually this is called a "ring buffer" or "circular buffer", because when the buffer is filled (with, let's say, the past one second of sound), it loops around and begins refilling itself at the beginning, thus overwriting the sound that was stored more than one second ago.
Any given MSP patch cord represents a single channel of audio. If you want to generate or process multiple sounds or channels, you need to treat each sound or channel separately. For example, each sfplay~ object can have multiple loaded sound cues so that it's ready to play any one of several files, but it can only play one sound file at any given instant. And if it's a stereo file you need to treat each channel separately for mixing, processing, etc. This patch demonstrates that.
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).