Though we've covered many CD burning topics here in the past, our Technical Support staff reports they regularly field questions about CD's being burned at the wrong pitch. The question would go something like this:

"I recorded a song in "Digital Cube-Logical Tools," bounced my mix down to a stereo file, and burned a CD. When I play back the CD, it sounds slower and pitched down. What happened? How can I fix this?"

This is something we frequently see in Tech Support, and the answer is always a "sample rate mismatch." There are several industry standards for sampling frequencies in audio: 44.1 kHz, 48 kHz, 88.2 kHz, and 96 kHz (rates well over 100 kHz are creeping up on us). This difference in sampling rates is often overlooked. What we frequently see is that your digital recording hardware is set to 48 kHz while recording into your DAW, OR the external source (DAT, ADAT, etc.) is recorded into your DAW via digital connections (S/PDIF, AES/EBU, TOSLink...), and that source was recorded at 48 kHz. Audio CD's play at 44.1 kHz, so when you import 48 kHz audio into your CD burning software (assuming you are even able to; not all software allows this) it simply changes it to 44.1 kHz to burn the CD. Play that CD and, sure enough, it does play slower.

We can use good old records (remember those?) as an analogy. What happens when you play the 45 rpm single on a record player that is set to 33rpm..? Presto! It plays slow and pitched down. Even though CD's are digital, they play at a certain speed (based on clock or sample rate) just like those good old records collecting dust behind your golf bag in the garage.

Solutions:

1. Record everything at 44.1 kHz. Verify hardware and software sampling rates BEFORE you start.

2. Convert existing 48 kHz files to 44.1 kHz. This is different from just changing the sample rate. A sample rate conversion effectively "resamples" your audio at a new rate while maintaining the speed and pitch of the old rate. Most professional DAW applications have some kind of sample rate conversion. Consult your manuals for more information. Some engineers do not like to do this type of sample rate conversion because it can have a detrimental effect on the quality of the audio. How subtle or severe this effect is depends on your system, the rates in question, and most importantly, upon the quality of the SRC's (Sample Rate Converter) algorithm for doing it.