Sampling Strings

The violin has been called the marvel of the woodcarvers art. Its a relatively small instrumenta mere fourteen inches longconstructed of spruce and maple
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Theviolin has been called the marvel of the woodcarver’s art.It’s a relatively small instrument—a mere fourteen incheslong—constructed of spruce and maple with an ebony fingerboard.Yet for more than four centuries, the violin has captivated listenersworldwide with its soaring tone and ability to evoke emotion. Everyoneknows what a violin looks like, but exactly how its astonishing tone isproduced remains acoustically inexplicable.

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Even with today’s technology, we cannot produce an instrumentwhose tonal qualities truly rival those of the great master builderslike Stradivari and Giuseppe Guarneri del Gesù. In much the sameway, a superb solo violin sample might be considered the touchstone ofthe sound designer’s art. Indeed, a sonically compelling set ofsamples of any of the solo strings—from violin and viola to celloand double bass—often seems beyond the grasp of even the mostdedicated sound designers.

In this article, we’ll take an up-close look at stringinstruments to see exactly why they are so difficult to sample.We’ll then discuss ways to work around these problems to ensurethat your string samples are the best they can possibly be. For themost part, a solo violin will serve as the primary example, though thetechniques we’ll be examining will work just as well for anyinstrument in the string family. Mind you, this article won’t dealwith string ensembles—that was covered in "All Together Now" inthe June 1998 EM. Be prepared: hard work lies ahead, but so does agreat finished string sample!

Unless you are intimately familiar with string performance techniques,I suggest you find a few choice recordings of some exceptional violinperformances. A particularly fine example is the 1980 Philips recordingof Bach’s Sonatas and Partitas for Solo Violin as performed byGidon Kremer, though there are hundreds of wonderful recordings out onCD now.

Regardless of what recording you listen to, you will be astounded bythe range, dynamics, and expressiveness of the violin. You’ll hearslurred notes, hammered notes, flying staccatos, ricochet bowings,glissandi, double stops, and more. Essentially, the immense variety oftimbre and effects that a violin produces occurs through a combinationof bow speed and the interruption of that speed by the pressure of theright index finger on the stick. The distance of the bow from thebridge is also a significant factor. It sounds simple, but adequatelyperforming such techniques demands an amazing amount of finesse anddexterity on the part of the performer, not to mention the ability toaccurately finger the notes with the left hand—all at the sametime!

While you don’t need to be an expert on classical bowingtechnique, it is important to be aware of the many ways a violin can bebowed and how each one affects the instrument’s sound. Most of thesampled solo strings in CD-ROM collections are limited to legatobowing, though some may include one or two other performing styles. Ifmore than one performing style is provided, they must be well matched.Otherwise, when you Velocity switch between samples, it’s quiteapparent that an entirely different set of sounds is being heard, thusscreaming at the listener: "This is a sampled string part!"

In the sidebar "Standard Bowing Terms,"you’ll find definitions of a few principal bowings that you shouldbe aware of. Although these definitions are not strict interpretationsof playing style, they should be adequate for the needs of the sounddesigner. (Classically trained violinists in the crowd, pleasedon’t write us nasty letters!) There are many variations on thesetechniques, and a skilled performer should be able to effortlessly movefrom one to another.

Ultimately—and I cannot stress this enough—your finishedsamples will depend upon the skills of your player and, moreimportantly, upon his or her cooperation and desire to do the jobright. Don’t even bother with a performer whose heart isn’tin the project.

Besides working with a skilled player, if you want a really greatsample set, you also need to be working with a better-than-averageinstrument. A well-crafted instrument will produce a more consistenttone, which is important because we will be grabbing only a limitednumber of representative samples. We must timbre-match our violin soundacross the sampler’s keyboard, so we want to start with aninstrument that has a consistent sound.

The instrument’s acoustics are another important factor toconsider. Every violin (and every other acoustic instrument, for thatmatter) radiates its fundamental tone and each set of harmonics fromdifferent areas of the body. A lovingly crafted violin is going to havea very nice balance between fundamental notes and overtones, as well asa wood body resonance somewhere between 500 and 600 Hz. While thefundamental is radiated more or less spherically, at frequencies above2,500 Hz, sound radiation is quite sensitive to direction. If theharmonics are well tuned (as they will be in a well-made violin), youstand a very good chance of placing your mics in one of theinstrument’s sweet spots.

On the other hand, a lesser-quality instrument might produce a setof harmonics that are not perfectly in tune with the fundamental. Ifyou place your mics in a position that is in-line with one or more ofthese strong overtones, your samples will end up having a thin, raspyquality. Those of us whose ears have not been trained to pick out thesesubtle tonal qualities will not recognize them until it’s toolate, and we may inadvertently place our microphones directly in theirpaths. What’s more, imagine an out-of-tune harmonic that is nowtransposed up one or two semitones—the sampling world’sequivalent of fingernails on a blackboard.

Almost every mediocre violin sample I have heard suffers from thesame problem: placing the mics too close to the instrument. Thistypically results in a sample with too much of a particular overtoneand an unnatural amount of body resonance. At first, this may seem togive your recording a nice "woody" tone; however, it’s going tosound strange when you start to transpose your samples up a semitone ortwo.

Even more disturbing is the fact that close-miking overemphasizesthe scrape of the bow on the strings. I’ve heard samples where thebow scrape is actually as loud as the note being played. While thescrape is an integral part of the sound of any bowed stringinstrument—and part of what separates a sampled violin from asynthesized one—it’s unnatural for this to be such a dominantpart of the sound. (Refer back to the sound of the violin on that CD Isuggested you purchase.) Add to that the same problem we had with theviolin body’s resonant peak: a loud bow scrape transposed up anddown a semitone or more will not sound natural. However, when ourfinished violin samples are played over accompaniment, thetransposition of a small (and even moderate) amount of bow noise willbe quite acceptable.

Unless you’re working in a soundproofed studio, you’llalso have to factor in the relative noise level of your recordingenvironment. If you’re working in a concert hall, it would seemlogical that you’d want to have your mics near the best seats inthe house: front row center, or about twenty feet from the stage.However, in most instances, that placement is just not practicalbecause all but the very best concert halls have some amount of ambientnoise (air conditioning vents, traffic, outside noise, etc.), and inall probability, the mics will need to be moved in. Ambient noise canalso a major problem when you’re recording at home.

So what can you do? If you place the mics too close, the violinwon’t sound natural when it’s transposed, and if the mics aretoo far away, you run the risk of capturing some unwanted room noise.My advice is to simply trust your ears. Walk around as your soloist isplaying and listen to the various characteristics of the sound. Whenyou have found a spot that pleases your ears, put the mics there, whichshould be somewhere in the area illustrated in Figure 1b. Then listenthrough a pair of headphones in mono to make absolutely sure no phasecancellation is occurring.

Of course, it also goes without saying that you need a pair ofexceptional mics to capture the sound of such a fine instrument. Ialways depend on my AKG 414s, but plenty of great mics are availablethese days that won’t set you back a year’s salary (andnaturally, quite a few that will). Most importantly, remember to doyour recording in stereo, even if you don’t think you’ll beusing stereo samples.

Depending upon the attitude of the player, the session itself can beeither a relaxing part of the project or a sure-fire migraine starter.If you have your performer’s complete cooperation,congratulations! Start by having them play a brief piece thatthey’re comfortable with, so you can get an idea of their playingstyle (three or four minutes is plenty). This is also a goodopportunity for you to check your mic placement and the overall qualityof the recording.

Next, have yourperformer demonstrate different bowing techniques based on thedescriptions discussed earlier. It’s very important for the playerto understand that each of the techniques must ultimately blendtogether to become a finished part of a virtual performance instrument,so radical changes in tone are not appropriate.

In order toensure you are getting the best material, you will probably have toallow your soloist to "slip their leash" a little. I believe that manysample libraries are far too hung up on consistency and have sacrificedsome amount of musicality. In any event, you’ll want to record atleast two or three takes of every note for each bowing technique.I’d recommend starting with smooth legato bowing, as this will laythe foundation for all further variations. While it isn’tnecessary to have your performer play every note, on every string, allthe way up the fingerboard, it makes sense to have them play at leastthree or four notes higher on each string so you will can choose theone that sounds best. As an example, when playing the lowest string onthe violin (the G string), have the performer play up to the E or F onthat string before switching to the next string up (D). On the topstring (E), you’ll want them to play up as high as possible whilestill maintaining a good tone.

Next comesanother critical decision: vibrato or no vibrato? I’ve longbelieved that no modulation source on a keyboard—up to andincluding a ribbon controller—can produce the richness of realplayer vibrato, particularly on a bowed string. But you’ll have tomake that determination for yourself. If you have plenty of time,record both. (Keep in mind that double-bass strings are really too fatto allow vibrato techniques on the lowest notes.)

If you decide touse vibrato, think about how deep you want it to be. Will the finalsampled sound be used for solo or ensemble work? For violin partsplayed over dense accompaniment, you’re going to want a nice, deepvibrato, whereas ensemble playing can benefit from something a bit moresubdued. Again, it’s your decision; but when in doubt, recordboth.

By the time youare done with your first chromatic run up the scales, you will have abetter idea of how long your session will ultimately take. If yourfirst pass took 30 minutes, that’s good. If it took an hour ormore and you’re not sure you really got the material you need,rewind your DAT and do a quick (but critical) listen. Don’t beafraid to bail on the project if things just aren’t sounding rightor you’re not getting the player’s full attention. Better toadmit defeat now than to end up with material you’ll never use,which is an expensive and frustrating proposition.

If you aregetting a good recording but the session is running long, try toreschedule a second session for a later date. From personal experience,I can tell you that anything you record after an hour and a half willvery likely be unusable. Imagine yourself in the performer’sposition: playing mindless scales for hours while someone tells you tomake it sound great. Your player is only human, so do your part to helpthem keep their sanity.

When and if youare ready to move on, continue recording scales of the various bowingtechniques. Remember to have the performer do a run playing pizzicatoand tremolando. There are actually two types of pizzicato: one in whichthe right hand plucks the note, and another in which the left handplucks the note. In the left-hand approach, the finger above the notebeing played does the plucking (e.g., if the left index finger isholding a D, the middle or ring finger is used for the pluck). Have theplayer try both, and decide which you like. For the double bass,you’ll want the right-handed finger pluck because you can also usethis for upright jazz bass parts.

Tremolando refersto a rapid back and forth bowing of the string, usually used to createtension in a solo part. Though this is more common in ensemble thansolo playing, it’s worth capturing because it can usually be donefairly quickly.

Finally, nodiscussion of the violin would be complete without mentioningharmonics. Almost everyone can identify guitar harmonics, but not manyare aware that a violin (or other bowed strings) can also produce suchunusual sounds. As with guitars, both natural and artificial harmonicsare available, but a thorough discussion of these is beyond the scopeof this article. If you are interested, have your performer demonstratesome harmonics for you, and then determine whether they are useful foryour applications.

At this point, we’ll assume that you have had at least one or twoexcellent recording sessions and that you have recordings you feelcomfortable with. Now comes the most agonizing part of all: weedingthrough the recording and importing the individual samples into yoursampler. Nothing will prepare you for how much work goes into this partof the project, but keep in mind that, as your "virtual violin" beginsto come to life, you’ll understand why it’s worth all theeffort.

Let’s consider againthe issue of stereo and mono samples. Even if you think that you willnever need a stereo violin, go ahead and create a few stereo samples,and then create mono versions of the same material. You will almostinstantly hear how much more life there is in the stereo version.Honestly, it’s worth the extra RAM and decreased polyphony. Afterall, RAM is pretty cheap these days, and you’ll be playing onlyone or two sampled notes at a time. Give it a try; you’ll be abeliever.

A little judicious use ofa good equalizer can help at this point. A few notes inevitably end upsounding somewhat brighter or darker than those around them,particularly as the player changes strings. I have also discovered thatgradually equalizing out some of the lower frequencies (below 180 Hz)as I move up through the highest notes of the violin’s range helpsto keep bow scrape to a minimum. For the very top notes, I might cut asmuch as 9 dB.

As an experiment, youmight even try an audio enhancement processor (BBE Sonic Maximizer orAphex Aural Exciter, for example) to give the samples some additionalsparkle. Just make sure you apply these effects discreetly. EQ andenhancement can also be done in the editing stage on your computer (ifyou’re using one) with plug-ins like DUY Shape, Waves Q10, andmany others. I never use compression on my samples, but that’s apersonal choice; use whatever you believe will give you the bestfinished product.

Here’s anotherimportant tip: don’t even consider looping your samples at thispoint. Just choose the best-sounding notes and keep on going. You mightwant to import more than one sample of a particular note (e.g., a D#played on the lowest string and then again on the next string).Digitize more samples than you believe you’ll ultimately need. Youdon’t have to decide exactly which ones to keep right now; youshould make that decision after you have all your samples safely tuckedaway on your hard drive. Also, be sure to save your material afterimporting every note or two, and if possible, make a backup copy. Somesamplers (like the Kurzweil K2500) have a "verify" function that makessure what is written to disk will be readable later. If your samplerhas such a feature, use it!

After you have finishedyour first complete set of multisamples, you can do the final selectionprocess. Build a keymap from the lowest to the highest notes,auditioning samples as you move up the keyboard. You might find thatyou are comfortable with some samples transposing a semitone up ordown, while in other instances, you might need two notes adjacent toeach other to adequately fit a specific range. The more samples youuse, the more expressive your final sample will be.

When you finally have a great set of samples, then you can tacklelooping. If you recorded with vibrato, your task will be easier becauseit’s pretty easy to see the individual vibrato cycles in a graphicwaveform display. Grab a cycle and loop it, using your ears to pick outthe loop points, and use a small amount of equal-power crossfading tosmooth out any tiny bumps or clicks.
If you recorded without vibrato, your challenge will be somewhatgreater because the timbre at the midpoint of your sample will rarelymatch the end point. You might want to try a short linear crossfade ofjust a few cycles several seconds into the sample, or you might findthat a 1- to 2-second equal-power crossfade is needed. There is no rulehere that covers all the bases. Just keep in mind that when you useyour violin sample in an actual performance (and add manual vibrato),your loops will be almost invisible to the listener. (For more in-depthinformation on looping techniques, see "In the Loop" in the September1996 issue of EM.)

I wish, for all our sakes, there were some simple techniques thatwould make producing a stunning set of samples faster and easier.Unfortunately, there aren’t any. In fact, by the end of thisproject—depending on your specific goals and your personal levelof perfectionism—you will doubtless have invested dozens of hours,maybe a hundred or more. Don’t try to do it in a day or even aweek. Creating anything of beauty usually takes a long time, and youjust can’t rush this kind of project.
But once you have built your virtual violin (or cello, or whatever),all that’s left to do is play and enjoy. All of your work isrewarded by having a great set of samples that will be available to youfor many years to come.

Jim Miller is afrequent contributor to EM and a freelance sound designer whose soundshave appeared in ROM-based instruments and sample libraries fromAlesis, Roland, Kurzweil, Sweetwater Sound, and manyothers.

Standard Bowing Terms
legato The most common technique, meaning "played smoothly,"with no exaggerated attack. This is the foundation of your sampledviolin sound.
détaché Similar to staccato and referring to a shortnote that has a more
pronounced attack.
martelé Also known as a "hammered" stroke, this isproduced by the pressure and somewhat fast release of the first fingeron the stick of the bow at the beginning of each stroke. It creates abrighter, more pronounced attack.
spiccato A bouncing staccato in which the bow is lifted off thestring between notes.
portato A light articulation of each note produced by pressureand release of the first finger without halting thebow.