Tag Archives: mix~

Abstraction for mixing or crossfading two audio signals

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This patch is functionally identical to the mix~ abstraction in Example 1; you can read its explanation there. It’s repeated here in order to begin a series of examples regarding “initialization”: setting up the initial state of your program the way you want it. This patch demonstrates the use of a # argument in an object box to designate a value that can be specified in the parent patch when this patch is used as an abstraction (an object in some other patch). When this patch is used as an object in another patch by typing its filename into an object box, whatever is typed in as the first argument in that object box will be used in place of the #1, wherever it appears in this patch. (Subsequent arguments in the parent patch could be accessed with #2, #3, etc.) If nothing is typed in as an argument in the parent patch, the # arguments will be replaced by the integer value 0.

In this example, the #1 argument means that the initial crossfade value (to specify the balance between the audio signals coming in the first two inlets) can be typed into the object box in the parent patch. Notice that if the user does not type in any argument, the default behavior of this patch will be to send out only the audio signal of the left inlet, because the crossfade value will be 0 by default, resulting in a multiplier of 1 for audio signal 1 and a multiplier of 0 for audio signal 2.

[You can read a thorough explanation of the # argument in an excerpt from the Max 4 manual regarding the changeable arguments $ and #.]

An important thing to notice in this abstraction is that it has been constructed in such a way that the crossfade value coming in the rightmost inlet can be provided either as a float or as a control signal. If a person just wants to set a static crossfade value, a float is sufficient. It can be typed in as an argument and/or provided in the right inlet. For a dynamically changing value, though, a control signal is better. If, in the parent patch, a MSP signal is connected to the rightmost inlet of this patch, then any typed-in argument (and any float in the right inlet) will be ignored by the right inlets of the -~ and *~ objects in this patch.

A useful subpatch for mixing and balancing two sounds

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To mix two sounds together equally, you just add them together. If you know that both sounds will frequently be at or near full amplitude (peak amplitude at or near 1) then you probably want to multiply each sound by 0.5 after you add them together, to avoid clipping. However, if you want to mix two sounds unequally, with one sound having a higher gain than the other, a good way to accomplish that is to give one sound a gain between 0 and 1 and give the other sound a gain that’s equal to 1 minus that amount. Thus, the sum of the two gain factors will always be 1, so the sum of the sounds will not clip. When sound A has a gain of 1, sound B will have a gain of 0, and vice versa. As one gain goes from 0 to 1, the gain of the other sound will go from 1 to 0, so you can use this method to create a smooth crossfade between two sounds.

This example employs that mixing technique and implements it as a patch that can be used as an object inside another patch. It’s handy for easily mixing and/or adjusting the balance of two audio signals. Save the patch as a file with a distinct and memorable name such as “mix~.maxpat” somewhere in the Max file search path. Then you can use it as a subpatch (also often called an “abstraction”) in any other patch just by making an object named “mix~”. The audio signals go into the left and middle inlets and the mix value from 0 to 1 goes into the right inlet. There are three ways to specify the balance: 1) as an argument typed into the object box, 2) as a float in the right inlet, or 3) as a signal in the right inlet. Using a signal to control mixing is the best choice if you intend to change the mix dynamically.

Whatever goes in the inlets of the mix~ object in the main patch comes out the corresponding inlet objects in the mix~ subpatch, and the mixed signal comes out the outlet. The sig~ object provides a constant signal in which every sample has the same value, in this case a constant value of 1. The argument #1 will be replaced by whatever is typed into the mix~ object box as an argument in the parent patch; if nothing is typed in, it will be 0, and if a signal is attached in the main patch then the signal value will be used. This allows the user to type in an argument to specify the initial balance value in one of the *~ objects, and the -~ object provides 1 minus that value to the other *~ object. That initial balance value can be replaced by sending in a float or a signal.