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Hier de mijne van Michael Manring, van Bass Player Online:
Fretless Intonation, Part 1
I get a lot of questions about intonation. I'm pretty happy about that, because in playing any fretless instrument, intonation is the challenge—and it's always nice when people ask the right questions. As anyone who has even dabbled with a fretless or upright will attest, playing the dang things in tune ain't easy. Not only is it physically difficult, but we're all used to hearing fretted bass, so intonation standards are high. Playing a fretless instrument takes commitment, and it's probably best to accept that you just won't be able to play a lot of things on a fretless that you can play on a fretted. Still, there are so many nuance possibilities on the fretless, so much room for color and expression, that the struggle—and even the occasional sour note—is well worth it.
Like so many musical skills, intonation is really about listening. We all have an inborn level of pitch sensitivity, and some are gifted (or cursed, depending on how you look at it) with the almost supernatural ability we call "perfect pitch"—but virtually everyone can improve with practice. A good place to start is to train your ear to hear the acoustic phenomenon called "beating." This occurs when two tones of nearly identical pitch are played together; it's an audible modulation or pulsing at the rate of the difference between the notes' frequencies. If the notes are nearly in tune with each other (meaning the frequency difference is small), the beating will be slow; if the pitches are further apart the beating will be faster. Beating occurs because the two sound waves reinforce each other when their peaks align and cancel each other when they are out of phase. Beating is most clearly heard in two simple tones with the same timbre. This is why a common bass-tuning method is to compare one string's 5th-fret harmonic with the next-highest string's 7th-fret harmonic. It's also an excellent way to learn to hear beating.
A little beating is actually a pleasant sound—in fact, it's the basis for chorus and flange effects—but when beating gets faster the notes start to become dissonant. Try the 5th/7th-fret-harmonic tuning method and listen for when the beating starts to become displeasing. It's more important, though, to concentrate on getting the two notes exactly in tune with no beating at all. (Turn off all effects when you practice intonation so you're hearing as pure a tone as possible.) Once you're comfortable with this exercise, try playing the G at the D string's 5th "fret" (from here on let's use the term "place") simultaneously with the open G. The beating probably won't be as clear with these full tones as it is with harmonics, so take your time and listen to how the two tones interact.
Once you're comfortable hearing beating between unisons, move on to other intervals. Intonation has to do with the relationships between notes, so it's always best to practice intonation with some kind of reference. Your intonation might sound fine when you're playing single-note lines by yourself, but when you go to a gig and suddenly have to play with other musicians, it can be a very different story. It's not quite as easy to hear beating in intervals other than unisons, but if you take your time and listen carefully, you'll hear a pitch location where each interval sounds most in tune. Your pitch reference for practicing can be any number of things, but it should be something that's reliably in tune—if you spend all your time practicing to an out-of-tune piano, you'll get really good at playing out of tune!
If you have a friend willing to sit and play scales along with you on a fixed-pitch instrument (like piano or guitar) you're in luck—but I'll suggest a few other options. One of the simplest pitch references is using your open strings. Just as we used the open G as a reference for the D string's G, you can use it as a reference for practically any other note on your E, A, and D strings. Try allowing your G string to ring while you play all the other G's on your bass—the 3rd and 15th places on the E string, the 10th and 22nd places on the A string, and so on. Then play all sorts of G scales on your E, A, and D strings against the open G—major, minor, pentatonic, etc. Do this very slowly, and for each note, listen for the pitch location that sounds best against the open string. It can be hard to hear 2nds, 7ths, and their compounds, but the other intervals should have a place that really feels like "home." Try the same thing using each of your other open strings as the reference; then try tuning your strings to other notes to give you additional key references—for example, tune your G string to A, or your D string to C#. Open strings are always available as references, but the drawback is you can only practice your intonation on the remaining strings.
Eventually you can do these exercises with a metronome if you like, but it's good to spend some time concentrating just on pitch without worrying about time at all—that's hard enough!
