Frequency Sweepers

The recent post over at wayne&wax on “treble culture” got me thinking back to a subject we talked about on the first day of my sound class this summer: mediation and frequency filtering.

Roughly speaking, human hearing ranges from 20Hz to 20 kHz (not usually that high, especially as you age, but that range is easy to remember). Within that range, you can hear certain frequencies better or worse than others (“better or worse” usually just referring to the perceived loudness of a given frequency). But, to re-quote Raymond Scott from an earlier post:

The composer must bear in mind that the radio listener does not hear music directly. He hears it only after the sound has passed through a microphone, amplifiers, transmission lines, radio transmitter, receiving set, and, finally, the loud speaker apparatus itself.

Each of these steps is a mediation, and with each and every mediation come changes. The fun part of being a student of media is the cultural/social/musical/etc. side of mediation, but there is a more physical result of mediation as well: each step changes the frequency makeup of the sounds that pass through it.

Microphones pick up (or don’t pick up) certain sounds, amplifiers emphasize or de-emphasize certain sounds, and so on. Wayne is interested in the results of a particular chain of mediation—the kind that ends up on a cell phone, lo-fi speakers, or other treble-y playback devices. These cultural devices affect how music is produced and vice versa.

Leaving the ethnomusicology to the ethnomusicologists, I want to share some videos I’ve found recently that are completely fascinating from the perspective of mediation as frequency filtering: sine sweeps.

There are a whole bunch of these videos on YouTube. People typically run a sine wave sweep on their sound systems to demonstrate an even frequency response; that is, at every frequency, you’ll hear roughly the same volume. Drops in volume indicate imperfect frequency response.

There is, of course, some irony in putting these videos on YouTube in the service of evidence. Editing Scott a little, it’s not hard to hear what changes result from the transmission of the sine sweep from the speakers, to the video camera, through the YouTube compression algorithms, through your computer speakers or headphones.

Even sine sweeps delivered directly to YouTube fall victim to aliasing (listen to the repeating rise towards the end of the clip, and watch out, it gets loud):

It’s worth following this vid to the actual page to read people’s comments about what sounds are and are not audible: