A UGen which determines the (lowest) index in a buffer at which the two neighboring values contain a given input signal. The output index is a decimal whose fractional part is suitable for linearly interpolating between the buffer slot values.

For example, if the Buffer contains values 3, 21, 25, 26 and the input signal has the value 22, then the output will be 1.25, because the value 22 is in-between the values stored at indices 1 and 2 and the linear location of 22 is one-quarter of the way along the interval between them: 21 * (1 - 0.25) + 25 * (1 - 0.75) = 22.

If the input value is smaller than the first sample, the output will be zero. If the input value is larger than any sample in the buffer, the output will be the buffer size minus one.

While designed for monophonic buffers, it works with multi-channel buffers by treating them as de-interleaved. For example, if the buffer has two frames and two channels, and the algorithm finds the frame 1 in channel 0, the reported index is 2 (frame * numChannels + channel).

IndexInBetween is the complement of the IndexL UGen.