More thinking on digital clocks, pitch problems, sample rates, and transfers from last week’s inSync (1/20/99). An inSync reader writes:
“Playback speed differences can occur even if the sample rates are the same for both the source and the DAW. If the DAW is looking at the external clock and that clock is different form the audio sample rate the audio will play at a different speed. You should use the external clock source when you do the transfer and the internal clock source when you play it in the DAW. This is easy to forget when you are in a hurry and forgetting to switch the clock source back to internal on the DAW will cause you playback speed problems.”
Editor’s note: While this is sometimes true and is certainly good advice all the time, it is quite often not the problem. In order to make a successful transfer of digital audio on most systems (successful meaning no clicks or pops) the clocks usually have to be synchronized, which means they are at exactly the same sample rate. If they are not exactly the same you run the risk of getting weird anomalies like clicks and pops. It is sometimes possible to do a transfer without your clock sources being synchronized and this “can” lead to pitch problems down the road, but for the most part (noticeable) pitch problems come from changing the sample rate as was outlined in the 1/20/99 inSync. Further, it is possible to leave your clock source set to external while playing back audio as long as the device supplying the clock stays on-line (though I don’t recommend doing this unless your setup requires it). If the clock source goes off line you will encounter drastic pitch problems that wouldn’t slip past even the most negligent engineer. People who build complex systems employ house sync generators that can supply word clock to their entire system. All devices stay on external sync all the time in these setups.