to cancelations. This leads to no sound on areas where the amplitudes cancel out one another; there will thus be silence in the middle of the crossfade. This occurrence is rare though since the parameters have to be the same. Commonly a crossfade will result in a gradual reduction in the amount of the sample whose pitch is lower, and an increase will be found on the pitch that is higher. The longer a crossfade, the more likely a problem will occur. One also does not want the effect of the crossfade to be very prominent in the middle of the notes, since if different notes are between the edit point there will be a time when both of the sounds can be heard simultaneously. This overlapping is not expected from a normal singing voice, no reference to Overtone singing. Crossfades can either be applied to a piece of music in real time, or it can be pre-calculated. Grandmaster Flash has been credited with the invention of the first crossfade by sourcing parts from a junkyard in the Bronx. It was initially an on/off toggle switch from an old microphone that he transformed into a left/right switch which allowed him to switch from one turntable to another, thereby avoiding a break in the music. However the earliest commercial documented example was designed by Richard Wadman, one of the founders of the British company Citronic. It was called the model SMP101, made about 1977, and had a crossfader that doubled as a L/R balance control or a crossfade between two inputs. Crossfade shapes When crossfading two signals that are being combined (mixed), the two fade curves can employ any of the shapes listed above (see #Shapes), such as linear, exponential, S-curve, etc. When the goal is to have the perceived loudness of the combined mix signal stay fairly constant across the full range of the mix, special shapes must be used, called "equal power" (or "constant power") shapes. Equal power shapes are based on audio power principles, particularly the fact that the power of an audio signal is proportional to the square of the amplitude. Many equal power shapes have the property that the mid point of the mix provides an amplitude multiplier of 0.707 (square root of one half) for both signals. A variety of equal power shapes are available, and the optimal shape will generally depend on the amount