Lesson 25 · Panning a mono signal - Build a WAV/PCM Toolkit

Panning a mono signal

Panning places a mono sound anywhere across the stereo field by giving each side a different share of the level. Today you build a simple linear pan, closing the DSP chapter.

The goal

Pan a mono signal into stereo using per-side gains from a pan position.

Start here - the target

TO DO

Scenario: A pan position sets the left and right gains

Giventhe mono sample 1000 and a pan position p in [-1, +1], with leftGain (1-p)/2 and rightGain (1+p)/2

Whenp is -1 (hard left), then +1 (hard right), then 0 (center), then +0.5

Thenthe (left, right) pairs are (1000, 0), (0, 1000), (500, 500), and (250, 750)

Andp at -1 sends the whole signal to the left channel and nothing to the right

Background

Panning positions a mono source in the stereo image by splitting its level between the two channels. A pan position p runs from -1 (hard left) through 0 (center) to +1 (hard right), and it sets two gains: leftGain = (1 - p)/2 and rightGain = (1 + p)/2. At p = -1 the left gain is 1 and the right is 0, so the sound is entirely on the left; at p = +1 it flips; at center each side gets half.

So a 1000 sample pans to (1000, 0) hard left, (0, 1000) hard right, (500, 500) center, and (250, 750) at p = +0.5 - biased right. This is the linear pan law, the simplest of several (constant-power panning keeps perceived loudness steady across the sweep by using a sine/cosine curve, a refinement you could add later). It is the last of the sample-math tools, and it turns the mono tones you are about to synthesize into signals you can place anywhere in the field.

Make it work

func pan(sample int, p float64) (left, right int) {
  lg := (1 - p) / 2       // p=-1 -> 1.0 ; p=+1 -> 0.0
  rg := (1 + p) / 2
  left = int(math.Round(float64(sample) * lg))
  right = int(math.Round(float64(sample) * rg))
  return
}

CheckpointDONE

You can pan a mono signal across the stereo field. The DSP chapter is complete; commit and stop here.