Archive for February 12th, 2012

Mysterious High-Frequency Spikes in Recorded Music

Those of you who have attended events at my house know that I use this version of Sting’s “Fields of Gold” as one of my reference tracks (especially for bass).

I happened to be analyzing those bass peaks today, and noticed intermittent frequency spiking at 19khz (see image). To my knowledge, this behavior doesn’t occur naturally – certainly not in music.

For example, while so-called “mosquito ring tones” (19 khz) are all the rage with kids, real mosquitos beat their wings at about 500 hz.

Sure, FM uses a 19khz carrier tone to indicate the presence of stereo information. And Rich Pell has documented this and other high-frequency peaks on CD recordings. He cites speculation regarding the presence of video gear during the recording process. I think that there may be a tie-in to digital-audio tape, but there’s certainly no “smoking gun” in that regard.

My gut tells me that these peaks are simply an artifact of the digital filtering process. They are aliasing or some other frequency fold. But this too is speculation.

One thing that is not speculation is that they are prolific. I frequently (sorry) encounter them in my measurements. What’s worse is that they exist in some high-resolution recordings from famous and well-regarded sources. I don’t want to turn this article into an expose, so I’ll just leave it at that.

The good news is that I believe that these glitches are sonically benign for 99%+ of adult listeners. We simply cannot hear these frequencies, especially when they are narrow-band and 20dB-or-more down from the musical peaks. But they may drive kids crazy.

Bob

Sunday, February 12th, 2012 Audiophile, Bob, Music, Technical 2 Comments