Revert change to Quantize invocation.

This is the 2nd time this has bitten me. For reasons I can't be bothered
to investigate much further the R900 decoder requires that preamble indexes
be offset by a full symbol length.

Reverting the previous commit that ignored a symbol length's worth of
samples when quantizing fixed this in the R900 decoder and broke everything
else because the R900 decoder still depends on this buffer for preamble
detection and does it's own signal processing for everything else. It's
preamble begins with 0's and can randomly pick up preambles without any
signal present for the first symbol. The rest of the protocols, not so much.

decode/decode.go

@@ -179,7 +179,7 @@ func (d Decoder) Decode(input []byte) []int {
 	d.Filter(d.Signal, d.Filtered)
 
 	// Perform bit-decision on new block.
-	Quantize(d.Filtered[d.DecCfg.SymbolLength:], d.Quantized[d.DecCfg.PacketLength:])
+	Quantize(d.Filtered, d.Quantized[d.DecCfg.PacketLength:])
 
 	// Pack the quantized signal into slices for searching.
 	d.Transpose(d.Quantized)
@@ -281,13 +281,13 @@ func (d *Decoder) Transpose(input []byte) {
 // buffer.
 func (d *Decoder) Search() (indexes []int) {
 	for symbolOffset, slice := range d.slices {
-		offset := 0
+		lastIdx := 0
 		idx := 0
 		for {
-			idx = d.preambleFinder.next(slice[offset:])
+			idx = d.preambleFinder.next(slice[lastIdx:])
 			if idx != -1 {
-				indexes = append(indexes, (offset+idx)*d.DecCfg.SymbolLength+symbolOffset)
-				offset += idx + 1
+				indexes = append(indexes, (lastIdx+idx)*d.DecCfg.SymbolLength+symbolOffset)
+				lastIdx += idx + 1
 			} else {
 				break
 			}

r900/r900.go

@@ -181,7 +181,7 @@ func (p Parser) Parse(indices []int) (msgs []parse.Message) {
 			break
 		}
 
-		payloadIdx := preambleIdx + preambleLength
+		payloadIdx := preambleIdx + preambleLength - p.Dec().DecCfg.SymbolLength
 		var digits string
 		for idx := 0; idx < PayloadSymbols*4*cfg.ChipLength; idx += chipLength * 4 {
 			qIdx := payloadIdx + idx