The wav.audio.php did not function properly, so I had to fix signed2hex.
It had two problems.
First, I concatenated $bits zeroes, then $bin, then took the right-most $bits elements, effectively left-padding the bin string with zeroes for shorter bins so I have a $bits-length bin.
Second, I prepended a zero to the hex string in the same function, when the length of the resulting hex string was an odd number. Sometimes the calculation came back with five hex characters, so in cases where length of hex was odd, I prepended zero, producing a hex number with even digits.
I have two valid wav files,. but can only get noise when I try combining them. I need some help.