You Say Vibrato, I Say Vibraato, Lets Call the Hole Thing f

On Vibrato...
The cello is loved as an instrument for its deep warmth and earthiness down low while also sounding beautifully and clearly with its high notes. I disagree with some who have said that it is much less wonderful in the middle range; though you may have to work against a spot where the note will naturally wolf, as I must on my instrument.

I read that the cello is the instrument which most closely matches the range of human voices. The cello is similar in sonority and range to a man's voice in its mid and lower registers, the woman's in it's higher. (Or more accurately, in the higher it has a fine, bright, pure quality of a boy whose voice has not yet changed. For the deeper soprano, one would better, the violin). It can be smooth or plesantly gravelly. Casals is quoted as advising to break the instrument, ie. play the cello with that signature, gravelly pull. If you aim for the deep gravely pull while playing in the mid range, it becomes just as wonderful as with its lowest soundings.

Another thing which will help you make terrific midrange sounds and, of course, throughout the whole range of the cello, is vibrato (he finally got to the subject!). It's been said that all art aspires to music and elsewhere that music immitates the voice (though at times it also follows after the dance, the march, the heartbeat or that other non-vertical rythmic activity for two.)

With vibrato (and glissando and careful dynamics), we can make the instrument almost sing and speak.

Now here's the rub, dude (and dudet)...
the cello can sound like an old, has-been, opera singer on a cruise ship or a young, sexy, head -turning youth.

Listen to some 15 year old sing and there will be a zip-fast, tight vibrato. Listen to the warbling of an older operatic and you'll hear a wider and slower vibrato.

The cello sounds you produce either way will have subconscious associations for the listeners. They will be reminded of one of these two types of people. (Or, of course, of a person within the wide range between these diametric two profiles.)

While Casals brought the cello to prominance, it was Feuermann who later became its greatest virtuoso. Feurmann played with a vibrato which tended toward fast and tight and it became faster and tighter after he played with Heifetz, imitating him, our finest string player. (Though my estimable teacher said that Feurmann may have surpassed him for the short time after he improved his technique by contact with Heifetz and before his untimely death. And no, I am not necessarily equating greatest cellist or string player with greatest virtuoso.)
Players say that it is important to have variety in vibrato and yes, it's great to emphasise a phrase or note with a wider, slower vibrato but it should be as a coloring from the so-called ideal.

Feuermann said that he always played with vibrato, even the 64th notes. I do too. Now, how is that possible? I'll get around to explaining.

But first, you must understand that when you play a note and vibrate or you play and fish arround for the exact tone, what the listener hears as the note is the highest part of your playing. (Or if you glisssand, the highest point of play upon stopping.) So, if you play with a vibrato, the highest part of the note is what registers as the tone you hit. If you hit the highest part first and then vibrate lower and back again, the listener registers the first thing you hit as the note. There are some who say that when you play with vibrato, it is more forgiving because the note can be anywhere within the range of your vibration... but no, if you want a truer, more beautiful sounding. If you just want nice, then it doesn't matter.

Two interesting points that should be mentioned here but I don't want to meander in dealing them now are that: one, with anchoring the thumb under the neck, especially with smaller hands, there is a tendency and ease to start the vibrato in the low or mid part of its range when streching with the higher fingers (such as from 2 to 4) because of the angle of holding the arm/hand; and two, Chinese bowed string instrumentalists vibrate from low to high, at least those I heard. Later and elsewhere, maybe, on these points.

If you do play a note hitting the pitch you want and then vibrate starting in the middle or low point of the vibration, it will somewhat sound as if an adjustment or second note is played... Like you did hit the note right and then you adjusted it to be too high immediately after.
Anyway, I promised that I would deal with vibrating on 64th notes. It's easy... just start the vibrato, that is, hit the note at the high point and bring it down. That's all you'll have time for. You make a rolling jesture with the finger from high to low (slightly) and it sounds wonderfully. You do this on every note. It becomes natural but it takes work. Now this is much easier if you don't anchor you thumb under the neck (or the thumb upon the string in the higher positions) while playing but that's another writing piece.

And how I found out Feurmann vibrated high to low took a bit of detective work on my part, (again, another time). Though I will say that going for the tight, fast vibrato was instinctual and the vibrating from the high point was due my teacher - both before I found that Feurmann did likewise.

And please enjoy your cello.