K404/K504 Assignment 4: More Sound File Processing

In this assignment, we'll look at four interesting Plug-Ins: The goal of the assignment is just to get a feel for each of these tools, and to make some sound that interests you. As always, try to imagine how you might use these sounds in your final project.

Granulation with RiverRun

First, we'll explore a Digital Performer plug-in, called RiverRun, that performs real-time granulation of sampled sound. To granulate a sound is to break it up into many tiny grains — each anywhere from a few milliseconds to about a half second in duration. Each grain is encased in an envelope and can be independently transposed. The grains flow out of the granulator in one or more streams, one grain after another. The time between successive grains determines the grain rate, or grain speed, which has a profound impact on the sound. If the grain rate is regular, you may hear a pitch with a frequency corresponding to the time between successive grains. If the grain rate is randomly varied, this pitch disappears.

Why would anyone want to granulate sound? The applications range from time-scaling audio to making a sustained sound out of a short snippet (e.g., a choral sustain from a guitar pluck) to creating interesting noisy or pulsed repetitive textures. Play with it and see.

Granular synthesis does the same thing, but instead of taking grains from a sound file, it synthesizes grains, using simple wavetable or FM synthesis. (We don't have a plug-in that does this.)

One of the first composers to explore granular synthesis, Barry Truax (from whose composition, Riverrun, the plug-in name, comes), likes to use granulation as an audio microscope, zooming in on sound and exploring its details in slow motion.

After you've played with RiverRun a bit, it'd be a good idea to read a more complete description of granular synthesis, such as the one provided in Computer Music Tutorial, by Curtis Roads (on permanent reserve for Hass).

Running RiverRun

I'll provide a few brief instructions to help you get started, but you have to experiment to really learn this plug-in. In the Documentation folder, there is a manual for the "Nautilus Bundle," which includes two other plug-ins besides RiverRun. Read the RiverRun section.

When you assign RiverRun as an insert for an audio track, you see the following window.

RiverRun screenshot

RiverRun works differently from other plug-ins, because it requires that you capture some sound into its waveform display. Then the sound is frozen, and you use the controls to traverse and granulate the sound. At that point, you don't even need to play the sequence — RiverRun always puts out sound, unless you bypass it.

Here's how to get started.

  1. In Digital Performer, create a mono audio track. Make sure that the track's output is stereo — it should read Analog 1-2.
  2. In the Mixing Board window, choose AudioEase > RiverRun as an insert effect for your track.
  3. There are two ways to capture sound into RiverRun. RiverRun can hold only about 3 seconds of audio.

  4. Now you can play with the sound. To tell RiverRun: "Please be quiet for a minute," use the Bypass button.
  5. Here are some problems to solve. When in doubt, read the manual (in the "Manuals and Demos" folder on your Desktop).

Saving RiverRun output

You can use RiverRun "live" in your sequence, but at some point you'll need to capture the sound it makes into a sound file. There are two ways to do this.
  1. Select a portion of the track that uses RiverRun, and choose Bounce to Disk from the Audio menu. Unfortunately, this doesn't seem to work as reliably as the next, more involved, method.
  2. Record the output of RiverRun into another track.

    1. Create a new stereo track, and record-enable it.
    2. Set its input to New Stereo Bundle > bus 1-2.
    3. Set the output of Riverrun's track to bus 1-2.
    4. If RiverRun's track has a soundbite in it, delete the soundbite.
    5. Rewind and record. (Press the Digital Performer record button, not RiverRun's record button.)

      While recording, you won't hear anything, but you'll see the waveform being written to your stereo track.

    6. Press stop, and do whatever you want with the soundbite that appears in the record-enabled track.

Spectral Processing: Spektral Delay

Spektral Delay is a plug-in for Digital Perfomer that lets you create all kinds of recirculating delay effects. Spektral Delay performs real-time FFT analysis and resynthesis of the audio in a track. It lets you manipulate the analysis data, prior to resynthesis, using the familiar model of a recirculating delay line (i.e., a delay line with feedback). The difference is that there is a separate delay line for each of the FFT frequency bands. You control the amount of delay and feedback for each band individually. It even has LFOs that modulate these values. You can also attenuate the amplitude of the signal for each band before it enters its delay line (performing an FFT-based EQ).

This is a big, complicated plug-in. Fortunately, the layout of the plug-in window helps you to visualize the signal flow, from left to right.

  1. The audio enters at the left, split into left and right channels. The left-most box displays a sonogram of the input, right after the FFT analysis is performed. Frequencies are graphed on the vertical axis; stronger frequency bands have brighter color.
  2. The box to the right lets you perform various canned spectral modifications of the FFT analysis data.
  3. The next box, labeled FILTER, lets you draw an attenuation curve across the frequency bands.
  4. The next box lets you draw the delay time for each frequency band. Click the mouse in the graph, and as you drag, you'll see the FREQUENCY and DELAYTIME readouts change to reflect your cursor position.
  5. The next box lets you set the amount of feedback for each delay line.
  6. The last box shows you a sonogram of the output, before resynthesis of the modified FFT data.

Spektral Delay screenshot

Some tips:

The Spektral Delay manual is in the "Manuals and Demos" folder.

Graphic EQ: Periscope

Periscope is a Digital Performer plug-in that performs a real-time FFT analysis on the audio in a track and lets you change the amplitudes of the FFT frequency bands before resynthesis. This amounts to a very flexible and precise graphic EQ.

In the Mixing Board window, choose AudioEase > Periscope as an insert effect for a track.

The top portion of the Periscope window gives you 32 frequency bands of EQ, with sliders to control the amount of boost or cut for each band. The bottom portion of the Periscope window lets you adjust the frequency range within which the 32 sliders operate. Drag the red and yellow needles around to set a range. Notice that the calibration of the sliders changes to show just frequencies within that range. Sliders on the left and right ends are low and high shelf EQs, respectively. Sliders in between are peak/notch EQs.

The fader edit mode buttons at the bottom right of the plug-in window control how your mouse movements affect the positions of the sliders. Free draw lets you, uh, draw a curve freely. Magnetic lets you drag one slider while its neighbors move to form a smooth curve. The magnetism knob controls the smoothness of the curve.

You also see, underneath the sliders, a real-time graph of the sound, post-EQ. (Actually, there are two graphs: the green graph shows peak amplitude, while the blue graph shows average amplitude.) This helps you evaluate the strength of frequency bands.

Periscope screenshot

Play around to see how dramatically you can change the sound. Unlike the Perigraphic EQ plug-ins, Periscope lets you make very steep, "brick wall," EQ shapes.

The manual is in the "Manuals and Demos" folder.

MasterWorks Compressor

MW Compressor is a Digital Performer plug-in that offers three separate compressors with crossover controls, allowing you to set the frequency range and compression characteristics of each band. Each frequency band can be soloed or muted, allowing you to audition them separately.

Here's what some of the controls do.

  1. Threshold: Determines the level above which the compressor will have an effect.
  2. Ratio: Determines the amount of compression on the signal over the threshold.
  3. Makeup Gain: Adds Gain to the signal after compression.
  4. Attack: Determines the time it takes for the compressor to react.
  5. Release: Determines the time it takes for the compressor attenuation to return to zero.

©2008, John Gibson, Christopher Cook