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Audio: Hearing... Visually!

Hal Robertson
June 2008

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What if I told you there was a revolutionary new way to visualize your audio recordings? A closely-guarded, secret technique that only the audio elite know and very few people can actually use. This secret technique is a recent discovery by a Swiss scientist who has gone into hiding due to government interference. But today, for only $19.95, I will email the secret to you. With this new visualization technique, you will make better audio edits and learn to manipulate audio in ways you never dreamed possible. But hurry, this offer won't last forever!

Audio Truth

Okay, the truth is that this visualization technique isn't new or secret or subject to government scrutiny. There are no scientists in hiding -at least none that I know of -and you don't have to send me $20 to find out, but the other stuff is true. This technique is spectrum analysis -or specifically, an audio spectrogram -and your audio editor may already have this feature buried somewhere inside it.

Remember VU meters? These glowing little boxes on audio equipment contained some volume level markings and a moving needle to indicate the loudness of your audio signal. They've recently come back in a retro sort of way, and we even emulate them in software, but the fact remains, they're not terribly accurate or responsive. Next came LED ladders, which are still in use. They are quicker and easier to read in the dark, but still only show signal volume in real-time. In the audio and video editing world, we're acquainted with the audio waveform -those squiggly lines on the screen that show us loud and soft portions throughout the recording. This is even more useful, as we can see gaps, changes and trends over time. If you zoom in to a small portion, you can even see drum beats, dialog and other sounds. On the downside, there is no real way to determine the frequency content of the sound, only volume.

Enter the spectrogram. Editors like Apple Soundtrack Pro, Sony Sound Forge and Adobe Soundbooth and Audition all have a built-in spectrum view. There are others too, but if your editor of choice doesn't offer this alternative view consider downloading the freeware program Audacity. It has a nice set of standard editing tools, is multitrack-ready and offers a basic spectrum view. Regardless of your platform, the spectrogram offers a new and powerful way to view and edit your audio tracks.

A New View

The audio spectrogram provides quite a bit of audio information, but it may take some time to figure out. As with a waveform view, you have volume and time information, which helps you identify sections of the recording. But instead of a simple up-and-down volume indicator, the spectrogram shows the intensity of sound across the spectrum through a colored vertical scale. Applying the visible color spectrum to audio, louder sounds are represented by reddish colors, while softer sounds lean toward the blue end of the scale. The first time you see an audio spectrogram, it may seem a little strange. You see the cursor moving through the length of the piece, but instead of seeing lines moving up and down, you're treated to a color show. It doesn't take long to figure out, and you will quickly learn to identify musical beats, individual instruments and other items.

Figure 1 shows the introduction to AC/DC's Back in Black. You can clearly see the opening count-in and where the guitars kick in. On further examination, it's pretty easy to pick out individual guitar notes, along with bass drum and snare hits, and later the vocals. Just as with a waveform view, you can also zoom into a specific area, in both the time and frequency domains. You'll have to do a little more mousing to navigate the spectrogram, but the information is all there. This puts a whole new twist on standard editing. Using the spectrum view, it's easy to find the downbeat of a musical section or beginning of the solo. This makes it easier to divide a musical piece for looping or rearranging. Vocals benefit, too. Now you can quickly find the take where the narrator used his best James Earl Jones voice.

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