As a cellist, I'm keenly aware of the limitations of most sample libraries dedicated to solo strings. Even with an extensive library containing multiple articulations (types of bowing), a given sample is a static entity. Expressive nuances that are easy and natural on a bowed instrument simply can't be achieved by triggering samples.
That's why I was eager to learn about the technology behind the Garritan Stradivari Solo Violin and Gofriller Solo Cello libraries. Though these libraries are based on samples of real instruments, advanced signal processing is used to give electronic musicians greater freedom of expression and to reproduce details of string performance that would be difficult or impossible to achieve using standard sample-playback techniques.
FIG. 1: Gofriller Solo Cello ships with Kontakt Player 2, a playback-only sampler. Effects can be added in the mixer panel (lower right).
We reviewed the Garritan Stradivari violin library in the August 2006 issue of EM (available online at www.emusician.com). Many of the features discussed in that review are carried over to Gofriller Solo Cello, though several minor enhancements have been added.
The End Pin
Gofriller Solo Cello occupies 509 MB of disk space and is played through Native Instruments Kontakt Player 2, which is installed along with the library (see Fig. 1). Online authorization through Native Instruments Service Center is required but painless. Gofriller Cello and Kontakt Player 2 are closely tied together via the latter's MIDI script feature, which allows developers to craft unique responses to incoming MIDI messages. Because of this, Gofriller Cello presumably won't be released for other platforms. This is not a big stumbling block, though, as Kontakt Player 2 can operate in standalone mode or in any of the major plug-in formats.
I used Gofriller Solo Cello on a 3 GHz Pentium 4 PC with 1 GB of RAM and Windows XP SP2, running it both as a plug-in in Steinberg Cubase 4 and as a standalone. I encountered no operational anomalies of any kind: the software was rock solid.
For this review, I beefed up my M-Audio Axiom 61 keyboard controller with an M-Audio EX-P Expression pedal. Although it would technically be possible to record tracks using Gofriller Cello with a plain MIDI keyboard and then add Expression (Control Change 11) and Channel Pressure data after the fact using a pencil tool, the spark of musical spontaneity would be lost. For practical purposes, an Expression pedal and a keyboard that transmits Channel Pressure should be considered necessities with the Garritan solo string libraries.
Gofriller Cello uses MIDI keys in the bottom octave to switch among a dozen different sound sets, modes, and articulations, such as pizzicato and harmonics. Tapping these keys and using MIDI Expression inputs are the extent of your control over Gofriller Cello — Kontakt Player 2 does not allow user editing of synthesis parameters such as filtering and envelope, though it does have some insert effects. Nor can you edit the MIDI script yourself.
Each note played on Gofriller Solo Cello (other than pizzicato) is assembled on the fly using several distinct sample layers. The attack layer contains only the initial sound of the bow addressing the string. This layer responds to Key Velocity, with low Velocities producing little or no attack noise and high Velocities producing a short and rather pronounced gritty noise. Repeated notes automatically alternate between two attack samples, which helps prevent the machine-gun effect and helps coax the ear into believing that the notes were played by alternating up- and down-bow strokes.
Note attacks blend seamlessly into the sustain layer. This layer crossfades between soft and loud samples under control of the Expression pedal. Ordinarily, crossfading between two sustaining pitched samples would produce phase cancellation artifacts, which would make the composite tone extremely unrealistic. One of the innovations in the Garritan solo string libraries is that the soft and loud samples in the sustain layer are phase aligned, allowing them to be crossfaded seamlessly (this technology was developed by Georgio Tommasini and Stefano Lucato). The phase alignment seems to work perfectly: I could detect no phase cancellation when I pumped the pedal.
That said, the difference in timbre between a cello bowed lightly and a cello bowed strongly is not great. Running a strongly bowed sample through a gentle 6 dB-per-octave nonresonant lowpass filter and closing the filter slightly to simulate soft bow strokes would give a very similar type of response.
The Gofriller Cello sustains are not looped. If you sustain a note for about six seconds, it will stop. Because a real cello runs out of bow after a few seconds, this makes sense. If you lift your finger before the end of the sustain, the sound transitions seamlessly to a release sample layer. But if you let the sustain run out while still holding the key, the release sample won't be triggered automatically; it will happen only when you lift your finger, which is very unrealistic.
The release samples add a couple of subtle touches of realism, however. First, notes that would resonate with the cello's open strings have slightly longer releases — not as long as on a real cello, but the difference is audible. Second, if you play a series of short notes that would be played on the same string on a cello, only the last note will have a release sample. But if you play two short notes that would be on different strings, both will be given release samples. No one but a string player would be likely to notice, but it does make a subliminal difference.
Listeners are more likely to notice the brief shifting noises that can be added to legato phrases. The amount of shift glissando between notes is controlled by overlap and Velocity. If the first note ends before the second begins, no glissando occurs. (On a real cello, of course, one can easily glissando into the first note in a phrase.) If one note is still sounding when the next begins, a high Velocity on the new note will produce little or no audible glissando, while a low Velocity will produce a realistic slide up or down to the new note. This effect is more complex acoustically than adding a pitch envelope; it really does sound to my ears like samples of positional shifts played on the fingerboard.
Vibrato is controlled in Gofriller Cello using a combination of Mod Wheel (for vibrato depth) and Channel Pressure (for speed). The vibrato sounds very good: it's not just a pitch change such as you'd get with a conventional pitch-modulation LFO, as there are realistic timbral changes as well.
To play music with Gofriller Cello, you'll need to learn some new techniques. Changes in bow pressure can be simulated using the Expression pedal, while vibrato is controlled with the left hand on the mod wheel and the right hand adding Channel Pressure. To add the sound of a shift between notes, you'll need to touch the new note lightly, even if the music is loud. Working the pedal and the mod wheel during every note will help maintain the illusion that an acoustic instrument is being played.
My initial response to Gofriller Cello was lukewarm, for three reasons. First, I'm a cellist, so my hopes and expectations were unrealistically high. Second, I hadn't yet hooked up the Expression pedal, so I was hearing only the soft sustain tones, which naturally have a higher proportion of bow noise. Third, I was listening to Gofriller in an unaccompanied setting, with no backing tracks.
Fortunately, Joe Cavanagh, one of Garritan's artists, had already recorded a MIDI file of Gofriller Cello playing Saint-Saëns's well-known solo, “The Swan.” I was already at work on a new synthesizer backing track for “The Swan,” so I was able to compare Gofriller Cello directly against my own performance of the same piece (see Web Clip 1). After I did some MIDI editing to get Gofriller Cello to sit better with my backing tracks, I was very pleasantly surprised by the quality of the sound. An educated ear can hear the difference between Gofriller and the real thing. On the other hand, my semipro performance had some imperfections from which Gofriller didn't suffer.
When soloed, the tone of Gofriller Cello is not as warm or gracious as I'd like. Reducing the amount of bow noise (using Control Change 15 messages) helps a little, but I can't help feeling that my own cello, which cost a mere $8,000 and was made in a factory in China, sounds as good as this lavishly praised 300-year-old instrument (see Fig. 2). (Garritan claims that its virtual instruments are not intended to replace real musicians.)
FIG. 2: The Gofriller cello, circa 1705, made in Venice, Italy.
A couple of the phase-aligned sustain tones have weird low-level harmonic artifacts. Middle C is especially bad in this respect, as it includes some brief artifacts that are distinctly flat. Using vibrato tends to mask these problems, but when played without vibrato, the tone of Gofriller Cello is slightly less stable than my own. The instability of a bowed tone naturally increases as the bow is slowed; faster bowing gives a tone that's purer and less wobbly. I'd speculate that the Gofriller samples may have been produced with a slow bow stroke in order to provide longer sustains without looping.
The high-Velocity attack samples seem a bit drawn out and scratchy to me. They're not a sound that I usually produce on a cello, except in staccato playing. Conversely, the quick pop of an on-the-string attack, which is normal in assertive phrasing, is not provided.
The con sordino (muted) samples are not different enough from the unmuted samples. They don't sound muted, just gently filtered. And the con sordino sample set uses the same bright, scratchy attack samples as the normal cello, which is surely a mistake. Gofriller Cello has no sul tasto (over the end of the fingerboard) samples. Sul tasto is a useful solo timbre in soft passages.
You can play double-stops (two notes at once) with this instrument, but the common technique of sustaining a note on one string while playing a moving line on an adjacent string is not possible. Smooth bowing transitions between strings, which require a momentary double-stop sonority, are also not possible. The long, ringing release tones of the open strings are not included. On the plus side, sustains of midrange tones played on a lower string than normal are included. Such tones are often used in cello playing, so it's great to have them.
Garritan's promotion for Gofriller Solo Cello promises “unprecedented control, unlimited variability, and extraordinary levels of realism, musicality, and expressiveness.” The level of control is definitely unprecedented: this software instrument is far more responsive to MIDI playing techniques than a conventional sampled instrument, and to that extent, its expressiveness is definitely enhanced, though perhaps not to an extraordinary level. The technology is promising, and I look forward to seeing further refinements.
The tone of Gofriller Cello is not impressive when soloed, but it can sound realistic when properly mixed within an ensemble. If you're doing computer-based orchestrations and need solo string voices to blend with a sampled string section, you may feel that Gofriller and Stradivari are gems. I shouldn't say this, but if you normally hire a few string players, these plug-ins will quickly pay for themselves.
Jim Aikin writes regularly about music technology for various magazines. In the mid-1960s, he studied privately with Laszlo Varga, who had been the principal cellist of the New York Philharmonic under Leonard Bernstein.
Gofriller Solo Cello 3.02
intelligent sample library
FEATURES3EASE OF USE4AUDIO QUALITY3VALUE4
RATING PRODUCTS FROM 1 TO 5
PROS: Playable and expressive. Sounds very plausible in a mix.
CONS: Tone lacks certain subtleties, especially when soloed.