Tremolo is pulsations of air pressure that cause a wavering effect to the loudness of the sound.
Vibrato is slight fluctuations of pitch produced by a slight wavering movement of part of the embouchure affecting the air stream.
The effective difference between the two terms is that tremolo refers to loudness and vibrato refers to pitch. Tremolo is oscillations in volume and tone, vibrato is oscillations of pitch.
In practice, however, both vibrato and tremolo can be applied to the same note at the same time. Then what do you call it? I call it vibrato. In my experience, the term vibrato is used more than the term tremolo for the harmonica to describe both of these techniques (whether used at the same time or not). I'll use "vibrato" whenever a pitch change is present, and tremolo when only volume oscillations are present, the pitch staying constant.
In addition, on the harmonica it is possible to produce oscillations of tone or timbre as well as volume and pitch by manipulating, principally the hands and tongue. This effect can affect volume in addition to timbre, and so becomes more difficult to properly classify. For example, hand effect "wah wah"s are commonly heard on the diatonic. Each "wah" is an opening of the hands, which results in a louder note with a different timbre, but essentially the same pitch. Since there is no pitch change present, I classify this effect as a tremolo.
Effective utilization of vibrato and tremolo is one of the most crucial elements of good tone.
If you gently say "ha ha ha" you can feel a pulsing of your diaphragm. It is this motion that drives the diaphragm tremolo.
If you say "ha ha ha" while breathing in you may feel a tugging or pulsing at the back of your throat. To keep the tremolo without pitch variations, open up your throat to keep the air stream from being pinched. If you pinch your throat to fluctuate the air stream, you are probably adding some pitch wavering, which means you are using a throat vibrato.
Throat vibrato is primarily associated with draw notes on holes 1-6 (not much on 7 because it doesn't bend too much), and the blow notes on holes 8-10. If you have good control, you can use vibrato blows 1-7 and draws 8-10. I found this to be easier once I could do overblows. The diaphragm is used to provide the playing pressure, the throat is used to smoothly pulse the air stream, and the throat works with the tongue to control the note pitch and the depth of the pitch oscillations.
The key to throat vibrato is a smooth oscillation of pitch and volume. Done poorly throat vibrato can sound chunky, and not smooth. Done well it sounds smooth and natural and wonderful. Strive for a sine-wave type continuous smoothness, with consistent pitch and volume changes. Rhythm is an important part of the vibrato. You can do vibrato at different speeds, so you should choose a speed that fits with the rhythm and feel of the music. The pulses of the vibrato should be made to divide the notes into even intervals to add to the rhythmic content of the music.
The classic way to get throat vibrato is to imitate a rapid fire machine gun (eh eh eh eh eh), like when you were a kid. Then do it inhaling instead of exhaling. It's the same throat motion that gets the throat vibrato. Work on it until all the chunkiness is gone, and it sounds as natural in your play as it does in a singer's voice. There is a tendency for throat noise to be heard during aggressive throat vibrato, especially when a mic is used and the sound is amplified. You should record yourself and listen to determine if the throat noise is audible or intrusive, and seek to minimize it.
A good way to get the feel of throat vibrato is to try put vibrato or even tremolo on the 3 draw 1/2 step (or even less) bend. Your throat is involved getting the bend initially, so there's some feel there before you go for the vibrato. Breathing from the diaphragm will help control the vibrato. There's always an interaction between the throat and diaphragm when doing a vibrato, since each is involved in controlling the air stream. For throat vibrato, obviously the emphasis is on the throat--but you'll probably notice some involvement of the diaphragm as well. As you pulse the diaphragm for tremolo on this note, the change in playing pressure coupled with the throat pulling the bend will tend to add a pitch fluctuation vibrato to the diaphragm tremolo.
Try playing the 3 draw 1/2 step bend amplified, but play softly. Practice very soft draw bends. At some point you'll notice what feels like a direct connection between your throat and the note. Every little nuance of throat motion will be reflected in the sound. Work on playing softly, with good note formation and support from your diaphragm. Then put some vibrato on the note by pulsing the air stream with your throat. The pitch will change up and down because you've got a hold of the bend with your throat. Keep at it, it's worth it!
How much should you use throat vibrato? Different players like different things, so it all depends. Often it is good to emulate what singers do, and start a note straight, then add vibrato toward the end of the note. Some players think there's no such thing as too much vibrato, they love it that much. Other players like to use it more sparingly, to add variety and contrast. I think you should use it a lot, but not all the time. Throat vibrato is one of the best things you can do to improve your tone, your control over the notes you play, and your focus on the connection between your playing and the response of the reeds.
The diaphragm provides the playing pressure support for the note, while the tongue and the throat work together to produce the desired pitch. In the case of bent draw notes, given a stable embouchure mouth, tongue, and throat position, the pitch of the note can be changed by changing the playing pressure. A gentle pulsing of the vocal tract below the throat can be caused by a nearly imperceptible pulsing of the diaphragm. Any more than VERY gentle nearly imperceptible movement of the diaphragm can cause an unacceptably large chunky vibrato that isn't smooth.
It is also possible to hit the bend using the throat and back part of the tongue to produce the pitch. This leaves the front part of the tongue free to manipulate the air stream and produce a kind of tongue vibrato. Articulations like "yo yo yo" and "oy oy oy" can help you identify the necessary tongue movements. Sometimes repeated "biting" type motions of the jaw or mouth and jaw can also be used to get some vibrato and tremolo type effects on bent notes.
Practice smoothly bending the blow notes down and back up over their full range. This will give you the feel of your tongue position, and how much small changes there affect the resulting pitch.
Make sure your notes are fully supported with your diaphragm so you don't lose your tone during bends, or when you waver the pitch by pulsing your throat or manipulating your mouth/tongue position.
Practice blow bend vibrato on holes 2 and 3 by going from the hole 2 and hole 3 full draw bend (2" and 3"') to blow vibrato for that hole. Your control over the air stream for the full draw bends can be maintained for the blow note vibrato by merely changing the breathing direction.
Alternate practicing on holes 7-10 and holes 1-6. Try to bring your tongue techniques from the upper hole blow bends down to your lower hole blow vibrato. With some practice, you should be able to slightly bend the low notes down in pitch, if you have enough diaphragm support. As you achieve some pitch variations on the low holes, bring that diaphragm support up to your high holes to add control to your smooth blow bends.
The high hole draw note vibrato poses a similar and symmetric difficulty to the low hole blow vibrato. First, concentrate on getting a good smooth tremolo on the volume for those notes. Gradually bring your throat and tongue into the tremolo and try to catch the critical pressure necessary to grab the reeds. Tiny movements and subtle control of the high hole draw notes can add a small amount of bend to those notes, and enable a vibrato effect.
Since the draw and blow notes in different cells on an unvalved harmonica like a diatonic bend different amounts for each note, you have to consciously adjust your technique to try to maintain a consistent vibrato for the various note types.
Draw and Blow Vibrato Consistency
One way to practice this is to use hole 7. Hole 7 seems to have some unique qualities. First, you can blow bend it, but only about a quarter tone--less than a full 1/2 step. This makes it a good candidate for blow vibrato, since some pitch variation room is there. The draw note doesn't really want to bend, but can be coaxed into moving a little bit easier than holes 8, 9, and 10. Since the depth of the blow bend is limited with respect to holes 8-10, the two vibratos--blow and draw--can be made to sound very symmetric. Practice getting a consistent, symmetric vibrato for the 7 blow and 7 draw, then move it up to the higher holes.
On the low holes (1-6) the odds are you've practiced and used draw note vibrato much more than blow note vibrato. Try to apply what you do with the draw note to your vibrato on the blow note. Practice going back and forth between a strong and controlled and rhythmic draw note vibrato and a similar blow note vibrato. Altering between the hole 2 draw and the hole 3 blow is effective for getting consistent vibrato because the pitch is the same.. go for the same tone as well. Hold the notes for a long time. Listen to how you shape the draw note--how the volume swells, when the vibrato begins, how the note pulses dynamically with the beat, how the sound trails off and whether the depth of the vibrato changes over the duration. Try to make the blow note do the same thing. The muscles, mouth position, and approach to the blow note will be quite different--pushing the pitch down instead of pulling it down--but try to make the adjustments so that the notes are symmetrical and consistent with each other, even if the playing isn't. I find that when I'm supporting the tiny blow bend on the low holes hard with my diaphragm, the tension makes it easy to produce a fast vibrato. So the speed doesn't naturally follow or flow from the draw note to the blow note--it has to be controlled to a slower rate to maintain the pulse and pace set by the draw note.
As you go back and forth between the draw vibrato and the blow vibrato you may find that what you can do with the blow vibrato feeds back into what you do do with the draw vibrato. You may make the pitch change depth more shallow, or you may change the vibrato rate to facilitate a consistent vibrato between the blow and draw. You may decide to use different kinds of draw note vibrato at different times, for different reasons--one type perhaps for consistency of phrasing in certain passages, another type perhaps for trying to rip a very emotional note out of a phrase.
Vibrato on overdraws are similar in technique to draw note throat vibrato. First you have to have a good stable overdraw. Then you have to have good subtle control over your throat vibrato. Practice draw note vibrato on the high holes to gain the fine control over those muscles you'll need for putting vibrato on the overdraw notes.
Since both blow and draw bends are available in every cell, the use of valves provides a good mechanism for increasing the depth of pitch changes on notes that normally don't bend much, and can aid in getting consistent symmetrical vibrato for blow and draw notes.
Single reed closing bends--those that are provided by valves--have a tendency to get weaker as the pitch is bent down. Effective use of the diaphragm and resonance is needed to support the note and keep the volume and tone consistent during the bend, and during pitch oscillations used for vibrato.
"But Ms. Tery, there was too much! Don't the others haveta have time to give their reports too?"
"Now Brassy, just think of something that stands out as important to you." And hopefully might be of some interest to the class, she thought. She motioned for him to come forward, and after a moment's pause, he finally obeyed.
"I learned that I haven't been paying enough attention to my blow vibrato," he said in the general direction of no one in particular, his eyes on his shoes. "I used to work on it more, but I forgot about it while worrying about overblows and some other stuff."
"Which of the teachers told you that?" she asked.
"I learned it from Joe Filisko. But he didn't tell me, he showed me."
"Oh, you mean you talked to him during one of the daily 3 hour teaching extravaganzas," she figured.
"No, it wasn't like that. I didn't know enough to ask him about that when I had a chance. He showed me up on stage, by playing his music."
"Well Brassy, don't make me keep asking. What did he show you?" She was getting a bit exasperated by now. Must be something in the air.
"He showed me how good blow vibratos can sound when you have enough control of them to push the pitch down a little in addition to oscillating the volume. That's a basic technique of draw note vibrato, but not so common on blow notes. It's a vibrato that can be done very fast too, it seems, probably faster than a draw vibrato."
"What do you think his secret is?" Ms. Tery asked.
"Well, the first thing you have to do is think about it and not ignore it," because otherwise you wouldn't even try to put it in, he thought. "And I think you have to have powerful blow notes. A lot of players work and spend so much time on the draws, the draw notes get very powerful, and the blows don't keep up. That's where I think overblows come in. The practicing of overblows--especially on harps not made by Joe!--helps develop very strong blows and control over the blow reed, which you have to "choke out" to let the draw reed sound the overblow note. I think it's because of getting in touch with the critical pressure..." she cut him off.
"Okay okay, never mind that." She sometimes grew weary of his long windedness. "Why would anyone care?"
"One of the side benefits of this overblow work is control over normal blow bends, of course, but another benefit is probably good power and control over blow note vibrato as well."
"Blow note vibrato isn't that difficult," she pointed out.
"Blow note diaphragm-based tremolo--as if you were saying 'ha ha ha'--the kind that oscillates volume only, and not pitch, is pretty easy. But getting any pitch shifting on the blow vibrato to compliment the throat vibrato on draw notes--that's more difficult."
"You can sit down now." she told him. He shuffled off back to his desk, and a part of him wished he was practicing instead of sitting in class.
But he loved the other kids.