Revert resampler pts length increase

The original length of pts made sense because when wantPos is a decimal position like 3.5, you want the window for quality 1 to contain positions 3 and 4. Having a window of 1 more doesn't make sense for that. My previous reasoning for increasing the window size was arguing from the point of wantPosition always being an integer value, which isn't the case.

resample.go

@@ -57,7 +57,7 @@ func ResampleRatio(quality int, ratio float64, s Streamer) *Resampler {
 		ratio: ratio,
 		buf1:  make([][2]float64, resamplerSingleBufferSize),
 		buf2:  make([][2]float64, resamplerSingleBufferSize),
-		pts:   make([]point, quality*2+1),
+		pts:   make([]point, quality*2),
 		off:   -resamplerSingleBufferSize,
 		pos:   0,
 		end:   math.MaxInt,
@@ -85,8 +85,8 @@ func (r *Resampler) Stream(samples [][2]float64) (n int, ok bool) {
 
 		// Determine the quality*2 closest sample positions for the interpolation.
 		// The window has length len(r.pts) and is centered around wantPos.
-		windowStart := int(wantPos) - len(r.pts)/2   // (inclusive)
-		windowEnd := int(wantPos) + len(r.pts)/2 + 1 // (exclusive)
+		windowStart := int(wantPos) - (len(r.pts)-1)/2 // (inclusive)
+		windowEnd := int(wantPos) + len(r.pts)/2 + 1   // (exclusive)
 
 		// Prepare the buffers.
 		if windowEnd >= r.off+resamplerSingleBufferSize {

resample_test.go

@@ -32,7 +32,7 @@ func TestResample(t *testing.T) {
 
 func resampleCorrect(quality int, old, new beep.SampleRate, p [][2]float64) [][2]float64 {
 	ratio := float64(old) / float64(new)
-	pts := make([]point, quality*2+1)
+	pts := make([]point, quality*2)
 	var resampled [][2]float64
 	for i := 0; ; i++ {
 		j := float64(i) * ratio