creative commons

To kick off a little experiment, I’ve thrown this blog under the Creative Commons license. Well, let’s see what happens….

playing in position pt. 1: don’t get lost

Still on hiatus from natural harmonics, and having proposed that the purpose of playing in position is not to get lost, let’s look at how this works in practice.

An element often neglected in those fingerboard diagrams is any indication of each finger’s function in position playing; in particular, the function of the first finger. The first finger is responsible for your bearings.
Let me say that with some emphasis:

In position playing the guitar player gets their bearing from their first finger.

Looking at piano, as a contrasting example, the pianist gets their bearing from the position of their thumbs. Thus, the pianist will shift their hand, aim to land their thumb on the appropriate key, and, while moving into position, the hand shape will be altered depending on the line/chord shape. A similar principle applies to the guitar and guitarist, except the player gets their bearings from their first finger.
One of the simplest ways to practice this is to play a line on a single string. You can do scales, arpeggios, or, my preferred pedagogical atom, a melody. Take something you’re familiar with; something with a mixture of intervals. Something like Somewhere Over the Rainbow or Morricone’s music from Cinema Paradiso:
Relax. Find a comfortable posture. Move your fingerboard hand into position. Choose, arbitrarily, one string. Stop the string only using the first finger and play.
Try and feel the movement of your body as you do this. Mentally note how each interval leap, each part of the fingerboard, feels different in your arm, shoulder, in your body. (If you’ve ever had problems playing with your eyes shut, this may be the time to try closing them again.)
Experiment with the motion of your arm. Try smooth motions, abrupt shifts; try slides, glissandi or play the notes staccato.
Try different phrasing; try different strings; try different melodies.
Try improvising on one string with the first finger stopping the string.
Have fun (but don’t over do these).

Attention: I have no knowledge of your physiology, your particular instrument, or your posture. Please, please, please, note that the following may not be applicable to your situations, and, at best, should be adapted to fit your your needs. Be careful and listen to your body: If it hurts, or it’s uncomfortable, stop and review.
Although I cannot give explicit advice about movement without making assumptions about your posture, and, consequently, your instrument and your body, keep in mind that position playing is “a framework for linking together small and large gestures”, and thus what we are practicing here is the macroscopic gestures. Generally speaking (and always adapt this advice based on your real-world posture, etc) the first finger’s movement should be macroscopic. Do not be afraid of broad, sweeping gestures. The movement should not come from the twist of your wrist. Try moving your arm, swing your elbow, work your shoulders, etc. You may feel your back, buttocks, legs affected by, or contributing, to this movement.
If your movement is hampered (e.g. your elbow is locked into your ribs), you may seriously want to consider reexamining your posture.

what’s in a name: free improvisation

What do you call this? Free improvisation? Open improvisation? Total improvisation? Each term comes with its baggage. If we wish for some kind of ahistorical, innocent purity, we ain’t gonna find it here. Each designation encapsulates a particular historical vantage point; comes with its own mythology. They are liberating in some ways, and oppressive in others. In short, these terms are political.
I don’t wish to fuel (local and transnational) factionalism in improvised music traditions (there’s certainly enough chauvinism and tribalism already) by opening up and inspecting these labels, but these labels confuse and alienate as much as they simplify and welcome. Coming to grips with these signifiers is part of the process of understanding the history and practice of improvised musics.

Take, for example, the twists and turns that’re found in Wikipedia’s entry on free improvisation (archived version dated October 12th 2006 ). According to the article:

…[in free improvisation] the musicians make an active effort to avoiding overt references to recognizable musical genres.
…[free improvisation] can be considered both as a technique (employed by any musician who wishes to disregard rigid genres and forms) and as a recognizable genre in its own right.
…[Derek Bailey claims that] the form [free improvisation] offers musicians more possibilities "per cubic second" than any genre….
…[free improvisation] "cannot be traced back to a genre other than the very generic term 'avant-garde.'"

So where is genre positioned in relationship to the term free improvisation? For that matter, what is the relationship between style and free improvisation?

"Free improvisation," as a style of music….
…Performers [in free improvisation] may choose to play in a certain style….
…it [is] difficult to pinpoint a single moment when the style [free improvisation] was "born".
…Bailey contends that free improvisation must have been the earliest musical style….
[Bailey:] "It [free improvisation] has no stylistic or idiomatic commitment."

Furthermore, the article confuses free improvisation as tradition (a sub-culture or sensibility that is more or less specific to a time and place, and/or a group of people/actors), and the technique, genre or style (an element or “piece” that can be executed or practiced within the bounds of one or more traditions). Without clarification, the article suggests that the latter pertains to the former. Beyond Wikipedia, the tangle of these, at best, overlapping terms is not particularly helped by the occasional sloppy, ad-hoc generalizations, and the various sects claiming this term as their own.
But I digress….
‘Free improvisation,’ confusingly, could be the term denoting assortment of overlapping or unrelated things. It designates a, perhaps local or perhaps transnational, (quasi-)tradition. It’s also a practice, perhaps associated with one or more of these traditions. It may be a technique. It may be a (quasi-)genre or (quasi-)idiom. Finally, it may signify an aspiration.
It is last of these meanings of free improvisation that I, simultaneously, am most sympathetic towards, and find illustrates a hazard of this term—the hazard in invoking the word ‘free.’ The question often asked, particularly by those who do not practice ‘free improvisation,’ is, can an improvisation be truly free? If ‘free’ stands for an aspiration—an ideal to strive towards—then this question becomes meaningless. It does not matter if absolute freedom is possible, it is the process of aiming for that goal that is of value. Yet ‘free’ in this sense has the same chimeric quality that plagues similar designations of cultural exchange such as ‘authenticity.’ All too easily I can transform this word into a flag to march under without any critical reflection whatsoever.

I should probably note that I generally avoid using the term free improvisation (I prefer the maybe slightly less problematic open improvisation). I do this not only because of some of the tribal reasons (which I’ve already bemoaned, and, I admit, I am somewhat guilty of), but because I often find that people, before hearing the music, already know what free improvisation sounds like. In other words, there’s a strong preconception about what the effect and practice that goes with that label….

accessories, embellishments and doodads: the capo

Just a brief post to say that I’ve, for the first time, started using a capo. …Well, it’s probably more accurate to say that I’ve started experimenting using a capo.
It probably does not help that I did not come though a tradition of guitar playing that uses these contraptions, nor was I ever a student guitar player who used these as training wheels, nonetheless I’m finding the whole experience slightly disorientating (understand that I’m not using this for the purpose of changing key). One thing in particular that I found surprising was how different an experience, physiologically/psychologically, it was to, say, retuning the strings.
Anyway, I’ll report back when I have something a little more substantive….

playing in position pt. 0, reasons for

Taking a break from looking at natural harmonics, let’s take a detour into fingerboard positions.

Playing in position is one of those staples of orthodox guitar technique (and the technique of many other string instruments). We all kinda have some notion what it is, but why do it? Candidate answers might include: (a) It facilitates faster playing, (b) it’s a more efficient or comfortable playing technique, or (c) once you memorize the positions, playing becomes easier.
There’s enough high-velocity players with extremely, let’s say, idiosyncratic techniques to throw serious doubt on (a). Given that everyone’s bodies are different, and guitars vary in shape and size, I’m always slightly suspicious of any claims of universal efficiency or comfort implied by (b).
As far as (c) goes, from a pedagogy standpoint, it is a popular answer. There’s a large amount of guitar tutor books and manuals that carry fingerboard diagrams of scales and arpeggios to be committed to memory. I’m skeptical. How many people can really be troubled to memorize every permutation of scales and arpeggios in a given position? And this approach may be fine when you’re dealing with a small number of patters (say, eight or nine permutations each of one major and one minor mode), but does it scale up? How many players find this ‘memorize and execute’ method useful? (That’s not a rhetorical question: I'm genuinely interested.)
I’m going to propose a slightly different reason for playing in position. To play in position is to prevent the guitarist (and their fingerboard hand) from getting lost. Position playing is a way of getting bearings, a method for practicing fingerboard gestures, and a framework for linking together small and large gestures. (BTW, I’m not claiming any universal utility, and I hope I’m not making a totalizing statement, but this does work for me, and I hope it will helpful in when we return to the topic of harmonics.)

the instrument: of cyborgs and performance

I’ve already written about the question of whether instruments were finite or bound. All I might add to that would be to say, somewhat whimsically, that it reminds me of the cosmologist imagining the universe to be finite, but boundless.

Off the bat, I reject the notion of heroic mastery of the instrument. As George E. Lewis argues, this view of the instrument mirrors certain political values.

…the hierarchical, highly moralistic model of ‘playing’ an instrument characteristic of Western musical pedagogy, where, in an eerie echo of a colonial “pioneer” experience, the achievement of “mastery” of an instrument is often presented as the the result of hard work, privation and striving for self-control.…

Lewis, 1999, p. 103.

The instrument is not a tool to be overcome or mastered. Nor is the instrument neutral or flavorless; something that it can be affected, but it itself cannot affect the music. In the case of the piano, for example, Stephen Travis Pope points out that:

…it has very concrete musical knowledge implicit in its tuning and user interface, and its unique but very limited timbre and envelope have a strong effect on the kind of music one makes with it. The role of the tool in the form result should be well established by now, and the myth of the “generic” of “uncoloring” tools must once and for all be laid to rest.

Stephen Travis Pope in Desain and Honing, 1993, p. 6.

So, where does that leave me…. If I was required to choose between the pro-instrument and the anti-instrument factions as posited by Derek Bailey (1992, pp. 98–102), I might tentatively align myself with the pro-instrument wing. I may, perhaps, be assuming that the pro-instrument wing would be more sympathetic towards the notion of virtuosity….
Let me put my cards on the table at this point and say, that for me, virtuosity is a significant element in how I relate to the instrument, how I relate to performance, and how I approach improvisation. Leave aside that vision of a raw, competitive, athletics concept, and I might argue for virtuosity as an interface between the instrument and the instrumentalist. If performance in general, and improvisation in particular, is the (re)enactment and (re)negotiation of identities, boundaries and relationships, then the space between actors (humyn and non-humyn) must be a site of (re)construction and (trans)formation.
I suppose what I might be arguing for is, taking my hat off to Donna Haraway, a cyborg improviser—the (un)natural, contradictory, partial identity that is techno-organism (Haraway, 1991). Should I insist on the stable category of humyn (me), or the stable category of the artifact (guitar), or the hard-edged boundary that separates us, no music can be made. It is in the re-negotiations, and the fluid motions, of the boundaries, the (temporary) creation of hybrids and networks that music (as side-effect) can be improvised.
Virtuosity, to me, means the confusion and connectedness of the (blurry) categories of the musical, the social, the cultural and the technological. On a good day I’m not sure where the cultural ends and the technological starts. Sometimes I wonder if my body stops at my fingertips, or whether it continues through to the fingerboard….

A final note: In someways, the guitar forms the interface (both the surface boundary and communication channel) between the guitarist and techno-cultural narratives. Narratives that enroll trans-corporeal characters such as tastes, sensibilities and tradition, and corporeal characters such as luthiers, audience members and other guitarists. The guitar is the terminal in that it is the communications channel between these actors and the guitarist; it is terminal in the sense that it is the momentarily frozen end point of these techno-cultural narratives; and it is the terminal which the guitarist can hold with two hands to complete the techno-cultural circuit.

references:

Bailey, Derek (1992), Improvisation: Its Nature and Practice in Music (London: British Library National Sound Archive).
Desain, Peter, and Henkjan Honing (eds.) (1993), ‘Putting Max in Perspective’, Editor’s Notes, Computer Music Journal (vol. 17 no. 2).
Haraway, Donna J. (1991), ‘A Cyborg Manifesto: Science, Technology, and Socialist-Feminism in the Late Twentieth Century’ in Simians, Cyborgs, and Women: The Reinvention of Nature (New York: Routledge).
Lewis, George E. (1999), ‘Interacting with Latter-Day Musical Automata’, Contemporary Music Review (vol. 18, pt. 3).

group improvisation: a question of leader(ship)

Oh boy, oh boy, oh boy. Something interesting happened in class this week. The proverbial genie is out of the bottle, and I’m not quite sure how I’m going to handle this. I don’t mean to sound negative; I’m fascinated that this turned up, and, anyway, we’d probably have to deal with this issue at some point… I just hoped that that some point would have been some point in the future (like, quite a few months into the future).

The word that encapsulates this issue is leader(ship).

Don’t see the problem?
Well…
That is one loaded word.
Did I say loaded? I meant there’s full-scale, über-density, hyper-congestion embedded in that little word.
Do we mean commander? The executive? Administrator or manager? The MC? Or the referee? The prompter? Possibly we mean trailblazer or the pathfinder. That who-is-followed, perhaps? (Tautological, I know.) Or might we mean coach, midwife, guide, sage?
I suppose because of my own views about group improvisation, and the particular practices and traditions I operate in and around of, I think, naively, that I was expecting this issue to be inconsequential to the students as well.
There you have it. The teacher was spectacularly wrong, flummoxed, fill-in-blank.
Okay. Now the bright side of all of this is the idea, unspoken as such by the students themselves but articulated nonetheless, that group improvisation is in some way society-in-miniature. A big topic that I need to return to in the future, but let me say this much here: Somewhere hiding behind the question of the leader(s) and of leadership was that notion that we can parse, discuss, and maybe understand collective improvisation sociologically. That maybe there is no difference between creative, musical interaction and social interaction in general.
When asked to think of the social or the political, we maybe instinctively think of the macro-social, the party-political, of contests, votes, elections, and ‘tough decisions.’ Of leaders and leadership. (And I think this was what the students were doing.) But the social and the political may also be the small, the intimate, the informal, the ad-hoc. Perhaps all we have to do, for the time being, is to imagine social contexts in which the concept of leadership is peripheral, or even irrelevant.

harmonics pt. 3: cataloging and improvisation

This is, for reasons I will outline below, going to be the final post on playing ‘natural’ (open-string) harmonics for a little while.
Before we develop a systematic technique (a mechanical-physiological interface) for playing harmonics, I recommend that you start improvising with what we’ve already covered. As I sometimes tell my students: You’re a newcomer only once—enjoy it.
In fact, go away and improvise on these harmonics right now.

Now what? Cataloging these harmonics. Itemize and group these, for example, by interval. Find the harmonics that make perfect fifths (they may not only be found in the obvious places). Find the fourths, thirds, seconds, unisons, octaves, etc. Now go away and improvise on one set of intervals (e.g. do an improvisation primarily using major thirds in harmonics).

Happy with those? Try improvisations using groups of two or more of these intervals (e.g. improvise on major thirds and minor sevenths).

Now try categorizing these harmonics by some other characteristic (e.g. tone).

Have fun, and take you’re time. You will do a lot of your searching and finding at this stage. Enjoy this process of discovery; you’ll only get this buzz once.

I’m taking a break from harmonics in order to get into a situation where we can systematically develop techniques for playing them: The mechanical-physiological aspect that, as I pointed out, “traditional guitar pedagogy neglects, and for which traditional notions of technique are ineffectual.” In order to begin developing this, I want to reexamine certain dogmas and rudiments of guitar technique. Specifically, I will make a detour into position playing.

Have fun and keep improvising.

harmonics pt. 2, the picking hand and

Following on from the discussion of the physics, and what the fretboard hand should be doing, let’s look at the picking hand when playing harmonics.

Many guitar players, when playing harmonics, will pick the string near the bridge. This maximizes the treble content of the sound, and you’re likely (for reason explored below) to ‘bring out’ the harmonics. Although this approach does work (if a bit of a kluge), the player will probably be moving the picking hand excessively when repositioning from ‘normal’ playing to playing harmonics. Many guitarists do not position the plectrum right at the bridge in their ‘rest position.’ In my case, for example, the plectrum is normally positioned somewhere between the 18th and 22nd fret. When playing harmonics, I generally shift this, not right up to the bridge, but to where either the 24th or 27th fret would reside: A shift of only 5 centimeters or so. With a little practice, the results sound almost as clear as (sometimes clearer than) the sound made if I were playing nearer the bridge.
Before we all rush off to try this, we need to understand how this works (mindlessly picking at the 24th fret will give mixed results).

Let’s look at a representation of playing a harmonic (A, B and C represent three possible picking positions):
Now, what kind of tone would you expect if picking at position B? Answer: A pretty poor quality tone since B coincides with one of the nodes. A node is the non-vibrating part of the string, so picking there would be counterproductive. Shifting the picking position towards A or C will get you much better results.
Now that you understand the principle, all that’s left is a little experimentation to find the optimal picking positions. Here’s the algorithm: Choose a harmonic to play; identify the node positions (recall the previous post on harmonics); try picking anywhere between nodes (keep in mind that your idea of optimal sound may not reside exactly half-way between nodes).
Once you've found optimal picking positions, you can begin to think about compromise positions. ‘Compromise’ in regard to your picking hand’s ‘rest position’ and in terms of maximizing the number of harmonics that sound in a given picking position. Again, in my case, for example, when playing harmonics, most of my picking is done at roughly the 24th fret and the 27th fret positions. Picking at the 24th fret position is acceptable (if not ideal) for harmonics up to about the 7th, but not for the 4th and 8th harmonics. On the other hand, picking at about the 27th fret position, the 4th and 8th harmonics sound acceptably, but the 5th and 6th do not. Thus, when playing harmonics, I’m shifting between those two picking positions depending on the harmonics I’m playing.

Incidentally, the position of the nodes also helps to explain why, in the case of guitars with magnetic pickups, different pickup settings will give radically different results. Again, there’ll be a temptation to just use the pickup nearest the bridge, but a little experimentation will yield viable alternatives.

Good luck and have fun in the search!

limits and boundaries: wikiality

An interesting and problematic article from Wikipedia on musical improvisation (archived version in case of changes).

Improvisation can be structured, with certain rules constraining the improvisation (for example, "make up a song about bicycles", "use these chord changes", and so on), or can have no such constraints.

As I wrote in a previous post there’s an assumption that structure comes from outside, and that ‘limits’ carry out that structuring. Additionally, the Wikipedia entry implies that improvisation without constraint results in a performance with no structure.
I don’t believe that this particular understanding of ‘structure’ is helpful to the practice of improvisation. Nor do I have much affinity with the desire for this ‘structure.’ As for alternative definitions of ‘structure,’ I’ll save that for a more extensive post….

A couple of other things about the article. How is it that the writers can state that improvisation has been “an integral part of music since the beginning of music,” yet suggest that improvisation is distinct or separate from the “conventional approach” to musical performance? I also wonder if improvisers would agree that what they do is play in an “offhand manner.”

harmonics pt. 1: where are they?

We’ve looked at the physics behind harmonics, but before I go into nitty-gritty technical matters, let’s just see how you go about finding those harmonics.

At the 12th fret position, place your finger lightly on the string. Pluck the string. Excellent: You’ve got the harmonic at twice the frequency of (one octave higher than) the fundamental.
Same again at the point above the 7th fret. You’ve trebled the frequency (gone one octave and a fifth higher).
Now, take position over the 5th fret. Quadrupled the frequency (two octaves).
Position over the 4th fret. Quintupled (two octaves plus a major third).

Fine, fine, fine, you say. We’ve all done this before. In fact, those are the harmonics that many guitarists use to tune their instruments. Ho-hum. Tell me something new.

Let’s take a few steps back and look again at the 12th fret harmonic. What we’re doing here is dividing the string’s length in half and effectively doubling the frequency.
The 12th fret position corresponds to the node (stationary points) in the modes of vibration we’re interested in (think back to the discussion of the physics behind all this).
Now look again at dividing the string’s length into thirds. The 7th fret position corresponds to one of two nodes. There should be another node since we’re dividing the string into three equal parts.
The other node is at the 19th fret position. Try placing your finger there to get the same harmonic.
Similarly, when dividing the string into quarters, there should be three nodes. They are at the 5th, 12th and 24th fret positions.
Note that the 12th fret position will not sound at two octaves since it is shared with the one octave harmonic. (These ‘unusable’ nodes will be present whenever a non-prime number division of the string length is made.)
Dividing the string into fifths gives you four nodes. They are at the 4th, 9th, 16th, 28th fret positions.
I leave it as an exercise to find the other harmonics (divide string by 6th, 7th, 8th...), but at some point you will stop getting useful results.

Okay, why all this information? Since some nodes will be technically more accessible or comfortable under certain circumstances, as you begin to explore playing harmonics, knowledge of these alternative positions will become valuable. As I will describe in a future post, knowledge of node positions will also inform your choice of where to pick the string.
Additionally, each different way of playing a harmonic has a different tonal quality. (Compare, for example, the 7th harmonic you get at the 2 2/3 and the 10th fret positions.)

Some final comments: The above recipe for finding the nodes (by dividing the string up into equal parts) assumes a perfectly flexible, zero diameter string with mass evenly distributed along it. When dealing with real-world guitar strings, you will find that the nodes are not exactly in the expected positions, especially with the upper harmonics, and when dealing with heavier gauge strings (I leave it as an interesting exercise to figure out why wound and unwound strings behave, in some cases, contrary to this). In addition to the above factors, the guitar’s action and neck relief will make the correspondence of fret and node position inexact: Use you’re ears and don’t stubbornly expect fret-positions to correspond.

the (finite?) instrument

A notion that turned up in the very first class this semester was that (experimental) improvisation broke boundaries, and that one of the boundaries in need of breaking was that of the instrument.
I’m interested in (and find problematic) this idea of the finite instrument, or of the instrument which needs to be (heroically) overcome. I think some of the students were confusing two separate ways in which the instrument might be bound and finite. An instrument may be finite in the sense that there are, perhaps, fixed channels, or specific protocols, for interfacing with it. It does not, however, follow that this restriction leads to finite possibilities in the aggregate behavior of the system or the resultant music.
There may only be six strings, twenty-plus frets and two hands, but I can’t begin to estimate the possibilities in the guitar-guitarist combination.

why improvise? redux

We addressed the question in class last week.
One person responded that improvisation was exciting, that you don’t (or can’t) get this kind of excitement elsewhere.
This reminds me of a discussion I had a few years ago with AMC—a friend and musician. We were discussing the purpose of improvisation, and, for AMC, spontaneity—the ‘real-time’ element—was an important part of the answer. The social dimension only really works because of the immediacy in interaction.
I’m now wondering if the notions of the social, the spontaneous, and the ‘edge’ are more closely tied together than I may have implied….

When the class moved on to ask in what ways improvisation was different from other forms of music making, a couple of interesting words turned up: ‘Perfection’ and ‘control.’ Composition, say, had the potential to move towards ‘perfection’ in a way that was, apparently, unavailable in improvisation. Additionally, as an improviser, you have less ‘control’ in comparison to someone who creates/manipulates texts/scores.
I apologize to the class for potentially misrepresenting them here (the word ‘perfection’ was, for example, quickly withdrawn), but I think these words are interesting. The words we use were, in many cases, developed to talk about different musical practices (e.g. a composition-interpretation model), and we sometimes stumble and fall over when talking about improvisation. I want to tackle these issues in more depth in a future post, but for now, all I want to say is that whatever ‘perfection’ is, and whatever ‘control’ might entail, each of these words carries with them a rich baggage of ideology and rhetoric which may or may not be helpful to the improviser.

harmonics pt. 0, the physics of

When, as in the practice of experimental improvisation, you are ‘allowed’ to do almost anything, there’s a distinct advantage in using a technique that limits your choices. Natural (open-string) harmonics fulfill the criteria of a limited palette, and, for those of us who came to improvisation via players like Derek Bailey, they, well, have the smell of a rich heritage.
Yet, after a cursory examination, this limited palette, on the contrary, turns out to be a large universe of possibilities. Possibilities that, let’s face it, traditional guitar pedagogy neglects, and for which traditional notions of technique are ineffectual.
So where does the aspiring guitarist start?
Before delving into the pedagogical and physiological aspects, I suggest they start with the physics of a vibrating string.

Note: To avoid confusion, I’m going to use ‘harmonic’ for the instrument playing technique and the resultant sound. I will use ‘overtone’ to talk about the mode of vibration.

There’s a familiar misconception that harmonics are ‘extra’ tones that somehow magically pop out when the string is played in a certain way. Harmonics are not ‘extra’ tones, but the result of the suppression of selected modes of vibration. In other words, harmonics are less than the unimpeded vibrating string.
A string will vibrate in a composite of several modes. A ideal (perfectly one-dimensional, evenly distributed mass, etc) string will vibrate in a composite of its fundamental and its overtones.
The above diagram represents the first six modes of vibration. I’ll refer to these as the 1st (or fundamental), 2nd, 3rd, etc. Note the integer sequence (1, 2, 3, 4, 5...) represented in the overtone series, and that each overtone effectively divides the string length (1/2, 1/3, 1/4, 1/5...). From this we can figure out where to semi-stop (lightly touch) the string to “play the harmonic.”
Let’s now see what happens when we do just that. As an example, if we semi-stop the string at the half-way point, the following modes of vibration are suppressed.
The supressed modes are, in this case, the odd ones (1st, 3rd, 5th...). All these are modes in which the string would have to move at the half-way point, but which it cannot since we have a finger pressed there.
The resultant vibration of the string is a composite of the following (2nd, 4th, 6th...).
Looking at half the string, we’re back to that integer sequence (1, 2, 3, 4, 5...).
In other words, we have effectively got a string that’s half the length, and a tone that’s twice the frequency (an octave higher in pitch). Also note that we have not added anything, we’ve merely masked out vibrations that would make the result sound like the fundamental.
I’ll leave it as an exercise to figure out how this applies when you semi-stop the string at other points (1/3, 2/3, 1/4, 3/4, 1/5, 2/5, 3/5, 4/5...).
Anyway, keep this picture in mind, and many of the problems in playing harmonics will be better addressed.

For more information checkout HyperPhysics’ articles on harmonics and sound and hearing.

limits and boundaries, purpose of

At some point or another improvisers come across the idea of ‘improvising within limits.’ Sometimes the rationale given for working within limits is that such limits give ‘structure,’ as if the presence of, or desire for, ‘structure’ (whatever that is) was somehow justification enough. A strangely circular logic that feels to me like the result of a composerly desire rather than a performerly one. (I will return to this idea of structure in a future post.)
Nevertheless, the success of schemes using limits and boundaries may convince the aspiring improviser to buy this justification.
What’s wrong here?
Well, nothing, except that the aspiring improviser may begin to worry more about the limits themselves rather than the qualities that made those improvisations successful. If they aren’t careful, instead of varied, high-contrast, information-rich performances, they will end up with performances that amount to little more than ‘Demonstrations of Limits.’
Schemes, strategies and scores that invoke limits on the improvisation are successful not because they impose ‘structure,’ but because they allow the improviser to take flight beyond known limits. They enable the permeation to other (technical or cultural) areas that had previously seemed inaccessible.
Or put it another way, temporary acknowledgment of one boundary allows for renegotiations of others.
For example, by improvising on a fixed set of pitch intervals, an improviser may discover a larger set of possibilities in other areas in, say, dynamics, timbre, complexity, spirituality or silliness.
Improvisation is a liminal act, and we are trying to find out exactly how porous the boundaries are. Limits should mean that other parameters (not under self-imposed bounds) should be explored, maybe uninhibited, bordering on the riotous, embracing diversity and, perhaps, contradiction.
With that in mind, we’re in a good position to examine and explore some of these limits and boundaries.

why improvise?

Of all the ways to practice, structure or perform music, why might we choose improvisation? There’s no right answer to this question, but addressing it may help us to understand what improvisation is. And finding a working definition of improvisation may help us focus our studies.
I’m not trying to to get dogmatic: there is, afterall, a multiplicity of constructive responses to this. Certainly, at least in my case, the reason for choosing improvisation as the primary mode for practicing music has changed (some times radically) over the years. Maybe seven years ago or so I might have approached this question in reference to, say, the “leap into the unknown” as Steve Lacy might have articulated it. I certainly still think about this “leap,” but now I would nominate an idea that was a peripheral issue back seven years ago as the primary reason I remain a card-carrying improviser: Improvisation is about creativity; about accepting the creative impulse in us and in others. It is, in other words, a social act. An act that is simultaneously of the creative and the political.

What happens is what happens; is what you have created; is what you have to work with. What matters is to listen, to watch, to add to what is happening rather that subtract from it—and avoid the reflex of trying to make it into somthing you think it ought to be, rather than letting it become what it can be.

From Anthony Frost and Ralph Yarrow (1990), Improvisation in Drama (London: MacMillan), pp. 2-3

What could be more humyn?