The word "tweak" can mean to twist or pull on something, but it also refers (and more commonly in every day usage) to making a minor adjustment to something, such as a musical composition.
When we're writing our own music it very commonly happens that something has to be "tweaked" to either get it to fit horizontally (melodically) with the other moving lines, to get it to fit vertically (harmonically) in the allowable space, to avoid forbidden consecutive parallel octaves or perfect 5ths (a diminished 5th preceded or followed by a perfect 5th is permissible, however), to keep it from violating some other rule of voice leading [See blog, Getting Started With Writing, Part XX], to do the unexpected for the sake of variety, or to eliminate an awkwardness in a moving bass line so it's easier for the feet to perform.
In this case tweaking is understood in a broad sense, and the tools of change are simple; we don't need a box full of them (photo) ... just the ability to make a change to take out, add, or otherwise change something in the notation of the score which can done easily and quickly using a notebook PC and music writing software or an online music writing application (like Noteflight) ... and knowing where and when to make it.
Editing a composition that we ourselves have written often uncovers places that need to be fixed, or tweaked, it's just the nature of the beast, and it reminds us a little of teaching the organ.
Teaching the organ to a student involves 2 processes: 1) identifying whatever, if anything, they're doing wrong, and 2) figuring out what in the blue blazes they have to do about it, to fix it.
Once the composer decides that some addition or correction is needed in the score and the solution is apparent, the actual work of making that change is relatively easy.
The free scores posted on this blog provide many examples of tweaking to get things to work better.
For example, sometimes a few notes in the subject itself are tweaked to introduce variety (Op. 2), to create room and get it to blend with the prevailing harmony (Op. 3, Op. 4), to keep it from crossing or forming a unison with an adjacent voice line or to make it more easily playable with another voice by the same hand (Op. 6), for the sake of variety (Op. 9), or to adapt it for the feet (Op. 13).
Sometimes even the rules of part writing are tweaked; when writing homophonically, where the top line reigns supreme in carrying the theme, one of the general rules of part writing is automatically tweaked (as in the Op. 2 Recessional) when we write homophonically and allow the soprano, alto, and tenor lines to exceed the upward limits of their voice ranges.
In the Op. 3 March, the opening statement of the theme where it appears in the top line had to be tweaked from the get-go to keep it from exceeding the upper limits of the soprano voice.
Sometimes a theme and an entire subsection of a work are both tweaked, as in the fugato section of the same work, simply to get the theme to work better with fugal procedure and to help eliminate monotony [See blog, Do The Unexpected].
In this passage the march theme which opens the work is tweaked in the fugato section to get it to work as a fugue subject; it first enters in the alto line and, surprise, it's in the key of Db Major!
Actually the Db Major entry here is a hold over from a previous draft of the work where the first entry of the subject was originally in the tonic key (Eb), but here it sounded so low in range that it caused the energy level from the previous section to drop when the music reduced down to only one voice; thus, this first entry of the subject was rewritten for 2 voices and transposed to a higher key (Db) where it could sound with more energy [See blog, Marching].
There's a lesson here, when we're writing an energetic march and working the theme as a fugato, to do what we have to do to keep the energy level from dropping.
In the same work, 2nd section, the 16 bar march theme is presented in inverse movement and introduced in the dominant key of Bb Major; here, instead of having this theme play out in Bb Major for the entire 16 bars this inverted theme is tweaked by dividing it in half; the first 8 bars (the first half) then remain in the dominant key of Bb Major and the 2nd 8 bars (the 2nd half) modulates to the key of C Major, again, to inject greater interest and help avoid monotony.
No voice in a fugue is somehow immune to this "tweaking;" sometimes it's found expedient to tweak even the subject itself, especially when writing in 4 parts on 2 staves where the subject incorporates disjunct motion and has a fairly wide leap in its melodic outline.
In the 10th variation of Op. 4 the theme and its inverse are worked as a 2 part canon at the octave against each other; both canonic lines are tweaked here with chromatic inflections; this not only gets both lines to fit harmonically with each other but it introduces a little flavor to the harmony and keeps it from sounding dull and monotonous, which is the chief danger to avoid when writing or improvising variations [See blog, Monotony].
The themes for the Op. 5 Prelude and Op. 6 "jig" Fugue were derived by tweaking the main theme of Op. 4 employing rhythmic transformation (same pitches in sequence but different note values); in the case of the prelude the upward leap of a major 6th in the Op. 4 theme was inverted, which transposed the bottom note an octave higher to create a minor 3rd leap downward to minimize disjunct motion in the tune [See blog, Inversions]; further tweaking of the tune with a triplet rhythm created an interesting, brand new melody that became the material for a completely new piece.
It was decided that the subject of the Op. 6 "jig" Fugue would retain the upward leap of a major 6th in its melodic outline because disjunct motion is desirable in a dance fugue like this; the challenge here with this type of subject is keeping the voice lines from crossing at the various entries and to prevent them from always forming unisons (approaching each other, then joining in the notation to share the same note).
Since the work has no pedal part and thus no independent staff for the bass line, the subject was therefore tweaked in the 4th entry of the opening exposition where it enters in the bass to keep it from crossing the tenor line; in the 2nd exposition the subject entering in the soprano was tweaked again to keep it from forming a unison with the alto line; in the 3rd exposition the subject in the bass was tweaked once more to keep it from forming a unison with the tenor line; the subject was tweaked once again in the 4th exposition where it enters in the alto to keep it playable within the span of an octave by the right hand and to prevent it from forming a unison with the soprano; the subject was tweaked yet again in the 5th exposition where it enters in the bass to keep it from crossing the tenor line and forming a unison with the alto.
This is a daring move, to try to write a 4 voice fugue on 2 staves using a subject with a leap of a major 6th in it [See blog, Audience Appeal]; tweaking its melodic line in the expositions like this is usually necessary to keep the voice lines from crossing, limiting their meeting at unisons, or to make it easier for smaller hands to play.
In this same Fugue both countersubjects are also tweaked in various places to provide better harmony, avoid dissonances, or to keep things more clear.
In the central 2 part canon of the Op. 9 Choral, one lone note in the soprano line (the follower) carrying the 1st theme had to be tweaked (moved to the nearest note that would work in the harmony) because, without changing that note, forbidden consecutive parallel octaves would result.
To get this central canon to work in harmony with itself and without parallel octaves it was necessary in fact to go back and tweak the 1st theme itself beginning with the opening section, after it was settled upon, and change its outline slightly; the original 1st theme, without tweaking, is then permitted to enter in the final section where the 2 themes are combined in the parallel major key (D Major).
In the Op. 10 Fugue, 1st exposition, 3rd entry of the subject, the 1st 2 notes of the subject are tweaked (raised a minor 3rd) to keep the 2nd note of the subject from descending outside the standard range of the tenor voice.
In the Op. 11 Fugue the 2nd theme, when it enters in the pedals, is tweaked (broken up) to where the higher notes are transposed an octave below to make it easier for the feet to play it.
In the Op. 13 "jig" Fugue one of the notes of the 1st countersubject is changed (tweaked) when it enters in the bass in the 4th exposition to facilitate a smoother execution on the pedals; the subject is also tweaked several times to get it to "fit" within the available space and once to avoid forbidden parallel octaves.
In the 2nd and 4th 3 part canons of the Op. 16 Canon, the left hand line had to be tweaked by transposing it an octave higher to get it out of the way of the other 2 moving lines.
In the Op. 19 Fugue, stretto section, the 1st countersubject had to be tweaked (held back from descending too low) to keep it from exceeding the standard downward range of the tenor voice, and one of the notes of the subject itself had to be tweaked (raised a minor 3rd) to get it to work with the prevailing harmony in the other voices.
In the Op. 21 Fugue, the subject in the soprano is tweaked (changed) to keep it from meeting the alto line at a unison; and in the pedal the subject in the bass is also tweaked (held back from rising too high) to keep it from crossing the tenor line and to avoid forbidden parallel octaves.
When we take a theme and tweak it by means of rhythmic transformation (same pitches in succession but different note values) we can come up with another interesting theme which can be used to build an entirely new composition.
The themes for both the Op. 5 Prelude Internationale and the Op. 6 "jig" Fugue were both derived this way by means of tweaking the main theme from Variations Op. 4 by rhythmic transformation.
This is also where the theme for the Op. 8 Diapason Movement came from, by means of tweaking (rhythmic transformation) of the 2nd theme from the Op. 7 Voluntary.
Someone should never think it unusual if, when they go over their work and edit their composition, that they find something about it which they overlooked and didn't catch before, that seems to cry out for additions or corrections.
We should count it all blessing, because it allows us to exercise one of the most wonderful, productive, and fascinating things about our own creativity [See blog, Revisions].
And there's no shame in that.