FIG. 2: This groove filter (bottom) was created from a bass loop’s sonogram (top) by isolating the string-slap portion of the sound (second from top), creating vertical bars (third from top), and adding some reverb for smoothing.

Stealing the groove. A nice thing about analyzing a rhythmic sound file is that its groove comes along for free. Fig. 2 shows the steps taken to analyze the groove of a 2-bar bass loop. At the top, the bass loop is analyzed in semitones at 32 pixels per beat. Low resolution is fine and even preferable here, because the goal is not to resynthesize the sound, but rather to find the accents.

This sound file is particularly easy to analyze, because though most of the action is in the bottom register, the string slap leaves a trail in the higher harmonics. Therefore, you can throw away the bottom part of the image and still retain the groove. This can be seen in the second frame from the top in the figure. In some cases, you may need to manually clean up the picture a little. The “Shorten” Hot Filter and “Noise Filter” options on the Processes submenu are helpful for that purpose.

The next step is to use the “Max” Hot Filter to turn the beats into bars, as shown in Fig. 2’s third frame. When you apply this particular effect, the program determines the brightest pixel in each column and gives all of the pixels in that column the same brightness value as the brightest pixel in their respective columns. (The Pitch and Harmonics submenu has a similar function for pitch.) Notice that the groove bars are rather narrow. You can use the “Reverb” Hot Filter with a small grid size to expand the bars and make a more effective filter (Fig. 2, bottom).

Once you have a groove filter, you can use it for filtering pictures or sound files. In either case, because the filter is imposing the groove, the effect works best on nonrhythmic source material. Try copying the groove filter to the Image Synth’s clipboard (type the C key), then opening MetaSynth’s Filter Palette and pasting the filter (type V). Change the original loop to noise in the Sample Editor, and apply the filter to the resulting noise sound file. You might mix this with the original sound file or use it as a source for MetaSynth’s Convolve and Formant Filter Morph operations. As an alternative, you could apply the groove bars to one of the other filters in the Filter Palette. Just type Shift+8 to filter whatever is in the Filter Palette with the groove-bars image on the clipboard.

BACK | NEXT

Reprinted with permission from Magazine, February, 2001
© 2001, Intertec Publishing, A Primedia Company All Rights Reserved