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GRM Tools - RTAS 1.0.3 and TDM 1.3.2 Reviews

January 1, 2002

Look around today, and you'll find a slew of plug-in processors that can chew up your sounds and spit out gigabytes of bliss and mayhem. After checking out a bunch, it's easy to become a tad jaded because you're probably hearing dozens of effects that sound the same. That won't be the case with GRM Tools, an intelligent selection of plug-ins for Digidesign's Pro Tools software that will delight and amuse you. Developed by the Groupe de Recherches Musicales (GRM; part of the Institut National de l'Audiovisuel [INA] in Paris), GRM Tools was designed by composers for composers. EM first reviewed GRM Tools in the January 1997 issue, and in the interim, GRM added refinements that make the GRM Tools bundles indispensable for the serious sound designer.

GRM Tools TDM 1.3.2 and GRM Tools RTAS 1.0.3 are available for the Mac; a PC version should be available by the time you read this. (A two-volume Mac and PC VST version is available from Steinberg.) The TDM and Real Time AudioSuite (RTAS) versions aren't identical; see the sidebar, “RTAS: A Sleeker Look,” to learn about the differences. I tested the program on a TDM system using a Mac G4/450 MHz with OS 9.1 running Pro Tools 5.1 with Pro Tools/24 Mixplus hardware. The TDM version requires a computer that will run Pro Tools software comfortably — I recommend nothing less than a PPC/400 MHz running OS 9.04.

GRM Tools includes plug-ins for comb and bandpass filtering, EQ, delay, Doppler effects, and three cryptic animals named Pitch Accum, Shuffling, and Freezing. I'll look at the general layout of GRM Tools TDM, each plug-in's main features, and a few application ideas.


Several GRM Tools plug-ins share the cursor-on-canvas approach of Arboretum's Hyperprism. Dragging the cursor, or Conducting Square (called the Conducting Ball in the RTAS version), controls at least two parameters at once. However, freely dragging the cursor around may not be ideal for controlling some plug-ins. By pressing the Control or Command key while dragging the mouse, you can limit the Conducting Square's movements to the horizontal or vertical axis. You can also reset the Conducting Square to a neutral location by holding down the Option key and clicking on the Conducting Square. If you prefer, you can bypass the conducting window and use the mouse on a slider or button to increment values, or double-click on a field to type in values.

All plug-ins come with 16 preset buttons. (GRM nomenclature leaves something to be desired. A preset can be a set of parameters assigned to 1 of 16 buttons or an automated segment that morphs between two button settings.) Clicking on a button once instantly loads factory or user-configured settings. You can also use a slider to adjust the transition time between presets from instantaneous to as long as 30 seconds. Each plug-in also includes a Super Slider: a long horizontal slider at the bottom of the console that lets you interpolate between preset locations manually. Eight preset markers along the Super Slider can be assigned to any of the 16 preset locations.

Whether you are dragging the cursor through the active field or using the Super Slider to morph between presets, each plug-in can become a performance instrument. Because you can automate each plug-in's parameter sliders in Pro Tools, it's possible to create unusual timbral shifts throughout a song.


GRM Tools TDM provides two versions of Comb Filter: single band and five band (see Fig. 1). In the latter, you can adjust the frequency of the five bands between 45 Hz and 20 kHz and apply resonance and a lowpass filter to each band. Master controls act globally on the resonators. Although you can get recognizable flanging effects with the plug-in, it could also serve as an excellent tool for formant synthesis. That would allow you to morph the timbral signature of, say, a door slam into that of a chime. It's also good for boosting bass frequencies to give the low end more oomph. In addition, I liked it for subtle treatments on a drum kit.

The Band Pass plug-in has two separate windows, which lets you use the Conducting Square for discrete, left- or right-channel applications. Band Pass offers an adjustable center frequency and bandwidth and has the ability to band-reject either channel. Each window has sliders to control the lowpass and highpass cutoff frequencies.

Equalizer provides 23 fixed-frequency filters (40 Hz to 13 kHz) in a graphic EQ layout. Intervals are a third of an octave apart with 12 dB of boost and 100 dB of cut available. Although there is no Conducting Square to control this plug-in, you can click and drag the mouse across the faders as a quick way to draw a setting. You can also use the Super Slider to control all faders at once and even automate fader movements for playback. However, the radical boost and cut capabilities combined with the transparent quality of its sound make the plug-in perfect for any subtle EQ chores.


Delay 24 provides a flexible environment for producing everything from classic delay to weird reverberant effects (see Fig. 2). Sounds can be repeated as many as 24 times with a maximum delay time of 683 ms. You specify how far apart successive delays will be and determine the amplitude of each successive delay.

As with any good delay unit, there's feedback control with the added convenience of cross-feedback control for stereo signals. Also, a random-delay feature includes a rate slider to control how often random numbers are generated. I used it to create odd shimmering effects on guitar and woodwinds. Delay 24 works wonderfully for changing the attack characteristics of staccato sources, such as plucked stringed instruments, and giving them a slow, scraping attack.


The Doppler plug-in lets you move sound around in space in real time by adjusting the speed, pitch, and stereo placement of the sound source. The Plug-In window shows the Conducting Square surrounded by a single small rectangular icon for mono signals or two icons for stereo signals (see Fig. 3). The icons circle the Conducting Square, giving you good visual reference for what's happening to the audio.

With Doppler, you can control how much the loudness and frequency change as the sound moves, and you can control the time the treated sound takes to catch up to the moving signal. Parameters such as Circle Frequency and Circle Amplitude let you control the amplitude of the sound's circular movement as well as how fast the sound rotates around the center. With stereo material, you can put one channel's rotation out of phase with the other, creating asynchronous movement of sound between the speakers. Although Doppler lets you achieve classic Leslie effects, its strength is in bringing three-dimensional qualities to a sound's movement.

I automated the Super Slider on a droning string section so that the sound slowly moved between the speakers without the panning becoming a distraction. I then created a churning alien-machine effect by setting the frequency to 100 percent and gradually raising the amplitude. I also got good results by experimenting with the feedback slider on wind-chime and BREAKing-glass samples.


One parameter-heavy plug-in is Pitch Accum, a potentially unruly beast of a harmony processor. The plug-in offers two independent channels, each with transpose, delay, and gain sliders. The Conducting Square is “wired” to the transpose sliders in the plug-in and can shift them up and down by 24 semitones (two octaves). You can select periodic waveforms for frequency modulation (sine, triangle, sawtooth, square, and pulse), and you can add random modulation. A Feedback slider can enhance reverberant and arpeggiator effects, and a mono and stereo parameter directs signals to both channels simultaneously or independently. Also, a Direct slider is used to lower the source signal in the mix.

Using the Window slider, you can select the length of the signal fragment being processed in real time. A Crossfade slider controls how the original signal overlaps with the processed one, and a Pitch Detector algorithm adjusts the timing of the fragments according to the input signal's frequency.

Pitch Accum functions as much more than a harmonizer, though it certainly can do that job. For example, I used the plug-in to slowly transform a soprano voice into a group of male voices. I also easily warped the sound into a bubbling soup of frequencies and then back to the original soprano. In addition, Pitch Accum was useful as a phrasing algorithm. I used it to eliminate the melodic component of a passage and then used the Window and Crossfade sliders to manipulate the sound's remaining rhythmic accents.


Shuffling was one of my favorite plug-ins. It lets you scramble an input signal's fragments and splice them back together. You can control the fragments' lengths and how far apart they will be and also adjust their pitches. To thicken a sound, nudge the Density slider to the right and add feedback. For silences between fragments, move the Density slider to the left.

Shuffling is useful for creating crowd effects or sporadic bursts of sound that pan between speakers. I loved the effect of applying it to a looped, melodic singing voice. I set a fast attack and release time (0 percent on the envelope parameter) and adjusted the Fragment parameter to match the source loop. With some fine-tuning, I was able to create a percussive semblance of the melody that I mixed with the original loop.

Although Shuffling is great, the plug-in I really became hooked on was Freezing. That algorithm snatches and loops brief segments of audio (see Fig. 4). Sliders control the number of loops (two, four, six, and eight repetitions), change the timing of loop playback, modify loop speed and duration, and tweak loop synchronization. The captured loop can also be scrubbed using the Conducting Square.

Freezing is the ultimate on-the-fly performance plug-in. It was especially useful on drum loops. I got a nice effect by duplicating a couple of drum tracks, dedicating a pair of tracks to the plug-in, and crossfading between dry and treated drums. I also used it to capture a quick bass drum and snare flurry and to play the selection with the Conducting Square and parameter sliders. That worked well at points in a song where some deconstruction seemed appropriate. Using the Conducting Square, I reduced the loop down to as little as 5 ms, scrubbed the segment to get flanging and tonal elements, and lengthened the loop to get recognizable snare hits. That also worked well with spoken and sung passages.

One drawback is that all GRM Tools plug-ins are quite DSP intensive. The largest segment I could freeze using my TDM system was 683 ms long. I'd have to use the RTAS version to get the three-second capture capability referred to in the manual. That is my only complaint about GRM Tools, but I hope the manufacturer will address it in future versions.


Like many musicians, I've combined analog synthesis and signal manipulation with the precision of digital recording and editing. I enjoy the rich sound and unpredictable nature of some analog approaches, even though I can't always replicate them. GRM Tools combines a flexible architecture with great-sounding algorithms that are never tedious. Their intelligent design connects them to the legacy of Pierre Schaeffer, whose spirit is still alive in the work of INA-GRM. But don't take this review as the final word. Download a two-week demo at the company's Web site, and you'll see what I mean. With the site's MP3 files and excellent support documentation, you'll be up and running in no time.

Alex Artaud is a musician, sound engineer, and writer living in Oakland, California.


GRM Tools RTAS 1.0.3 (Mac/Win) signal-processing plug-in bundle $349

GRM Tools TDM 1.3.2 (Mac/Win) signal-processing plug-in bundle $459



PROS: Intuitive. Flexible interface. Ability to morph between presets. Unusual algorithms. Ability to automate performance.

CONS: No Mix feature in TDM version. Very DSP-intensive algorithms.


GRM/Electronic Music Foundation
tel. (888) 749-9998 or (518) 434-4110


The GRM Tools TDM version has a decent user interface, but the RTAS version is a big improvement (see Fig. A). The RTAS plug-ins also provide operational advantages that TDM-only users may miss. For starters, RTAS users won't experience some TDM DSP limitations: the RTAS version offers as many as 128 delays in its Delays plug-in; the TDM version provides a maximum of 24. Also, most RTAS plug-ins cover a wider range of frequencies, and all have a Mix feature. The omission of Mix from the TDM version is a mystery.

The RTAS version is easier on the eyes. The darker control surface makes reading the parameters easier, as well as the added color in some of the plug-ins, such as Doppler.

GRM Tools RTAS is definitely a great value for host-based systems, especially if you have a fast dual-processor Mac. Even if you do have Pro Tools hardware, the RTAS version may be a better way to go. Just be prepared for the plug-ins to grab your computer's processing resources in a big way.

Minimum System Requirements


MAC: PPC 604e/200; 128 MB RAM; OS 9.04;
Pro Tools LE

PC: Pentium III/450; 128 MB RAM;
Windows 98/SE; Pro Tools LE


MAC: G3/300; 256 MB RAM; OS 9.04;
Pro Tools hardware

PC: Pentium III/450; 256 MB RAM;
Windows 2000/SP1; Pro Tools hardware

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