Seeing Musical Features in a Spectrogram (Bridge Over Troubled Water)

Audience clapping

Piano notes

This article walks you through an example (Bridge Over Troubled Water) of using a C-Ur-Sound spectrogram to see the notes in a recording. This spectrogram is in C-Ur-Sound's Gallery, so as you read the article, I think you'll want to "follow along", viewing the spectrogram in C-Ur-Sound yourself using C-Ur-Sound's Gallery feature (which works even in free Demo Mode). You'll probably want to listen to the song too; you can find the MP3 at Amazon here.

OK, let's dive in. On the right is a C-Ur-Sound spectrogram of the first few seconds of Bridge Over Troubled Water.

First notice the major features of the picture: The broad horizontal band across the upper half of the picture, that looks like red paint spatters over green spatters, is the sound of the audience clapping. The thin horizontal lines (mostly green, or red for the loudest ones) in the lower half of the picture are musical notes (piano in this case).

Identify a Feature: 3 Repeated Notes

Next, let's relate a prominent feature of the picture to the actual sound. Magenta is the loudest color in a C-Ur-Sound spectrogram, so looking for a loud feature we'll be able to hear easily, we see these three repeated magenta notes at the beginning:

We know these three notes are the same repeating note because they're all at the same horizontal level, not moving up or down. Rest your mouse on any of these notes (in C-Ur-Sound, not on this Web page), placing the pointer on the narrow trailing part of the note to make sure it's on exactly the right pitch, and C-Ur-Sound's lower-left status pane will show you that the pitch of these notes is G5, i.e. the "G" 1-1/2 octaves above Middle C.

Now let's figure out how fast these three notes are. Place your mouse on the beginning (the left edge) of the 1st note (in C-Ur-Sound) and then on the beginning of the 3rd note. C-Ur-Sound's status pane shows you that the 1st note starts at time 0.40 sec and the 3rd note starts at time 1.75 sec, so the 1st and 3rd notes are about 1.35 seconds apart. Also, you can see that the 2nd note isn't halfway between the 1st and 3rd notes; it's "late", closer to the 3rd note. Hopefully this gives you an idea of about how fast these 3 G's should sound and what their rhythm should be.

Now listen to the first couple of seconds of Bridge (using your favorite MP3 player program; C-Ur-Sound isn't a player). Hopefully you can hear these three notes we've been looking at; they're the first high, strong piano melody notes.

Seeing the Beats

Whenever you "find the beat" in music, you're finding a regular repeating time pattern that the notes fit into. When you listen to music, you do this without thinking. To see the beats in a spectrogram, you have to learn to see these same patterns with your eyes.

To find rhythmic points in the music, look for the beginnings of notes and for vertical lines marking percussive sound at a particular instant. Here are the rhythmic points I see in the first few seconds of Bridge. Notice that I've switched C-Ur-Sound's Time zoom to "stretched" to see the rhythm details better:

Now I need to fit a beat to these rhythmic points. In this case most of the rhythmic points are the same time-distance apart (about 0.35 sec), so this is an easy example. Based on the sound of this song and my experience with musical beats in general, I decide that this 0.35 sec time distance represents a half-beat rather than a whole beat. So here's how I see the first few beats, labeled here with the conventional "1 & 2 & 3 & 4 &" counting pattern:

Conclusion

So, in this article we identified notes and beats in a C-Ur-Sound spectrogram. I'm afraid my detailed how-to description might make this sound tedious. With some practice, though, I find I've learned to "read" a C-Ur-Sound spectrogram easily, and it helps me see notes I'm having a hard time hearing.