JAZZ AND FOLK MUSIC.
Jazz is a form of folk music, thus Jazz bands and folk bands and their music have certain aspects in common, including an oral tradition and history. However, it is common to find books of folk music, written out in standard notation. This however, only gives half the story. If you play the notes as written, it isn't folk music. Some years ago I went to a concert given by a well-known folk fiddler, well I suppose it was more a workshop than a concert. One very interesting part was where he took some well-known folk tunes that were claimed by the English, Irish, Scottish and Americans as originally there is, and played each tune in the style of that country's music. The notes with the same, but the tunes were completely different. This is also the case with jazz tunes and their notation. The differences were in the bowing, the rhythms and ornamentation. Writing down music has similar problem to try to indicate the accidents and dialects of region just in the printed word. Unless you are already familiar with the accent and dialect, there's virtually no way you can recreate it in your mind or speak in the appropriate accent when reading a book. The same applies to music.
Some people think that this doesn't apply to classical music, just because it's normal for classical music to be written down and performed correctly from the written form. But that isn't correct, it done because the dialect of the musical form is standardised. 10 different string quartets can sit down to play Haydn string Quartet, and the performance of each one will be very similar. Because of the age of the music there is a high degree of standardisation that has been taught by the music colleges and is evident in listening to recorded performances.
As you move through Beethoven, Elgar, Shostakovich and then on to the recent composer's, this level of standardisation decreases hear more variation between performances of a given string quartet. This standardisation though, only released to a single point in time. Listen to the recordings of some of the famous string quartets of the 1940s or 1950s, and putting the recording quality aside, the performances are often 1 million miles away from a modern performance. This proves that the style of the music cannot be defined entirely by the written notation.
Even in classical concert music, there can be things that can't be conveyed by musical notation, such as the fermatas of the conventional Italian operatic aria, the early 2nd beat of the correctly played Viennese waltz, the rubatos traditional in the performance of Chopin's piano pieces and the only partly marked change in tempi of Hungarian music. In each case these are necessary elements of the musical performance, yet the score only gives a vague approximation to their correct method performance. As I've said above, the further away from the long and precise traditions of European concert music, the less is it possible to write a score that accurately depicts what is wanted of the music.
This is evident even in present-day pop music, where the scores never say that the singer has to pronounce the word in a strange mid Atlantic accident, with certain words pronounced neither in the English or the American way. Similarly, folksongs tend to be sung in the rural and agricultural accident of the country, so that with English there tends to be a pronunciation that is foreign to most of the singers, who may well be speaking in a good BBC accident, but would sound totally ludicrous singing the average folksong or jazz ballad with such a pronunciation. So in singing, there's a whole new language and pronunciation to be learnt even before getting to the music. When it gets to jazz vocals, the slides and bending of notes is more connected with gospel singing all the complex warbling is of the Arab and Muslim artforms, which defy scoring.
Traditional musical notation specifies the sound value of music in relation to duration, pitch and intensity. Written music plots the sound rather mathematically, not so very far away from a graphical representation. But much of music is not simple in its mathematical form, and can't, outside the formal classical concert repertoire, be interpreted by simple divisions into 2, 4, 6 or 8.
If one interprets a notation symbol exactly, the note will remain a constant pitch and a constant degree of loudness and softness throughout its duration. There may be crescendo and diminuendo markings, but these are very broadbrush. When playing a single note, especially if it is a long note, as a member of the string quartet, various things can change through the duration of that note. The amount of attack, the amount of vibrato can increase, decrease, or have a sudden spike in intensity; the volume may change several times through the note, as may the tonality of the oak caused by variation in bow pressure or moving the bow closer or further from the bridge. If one is playing jazz style music, then the actual picture of the note may not remain constant, for example gradually homing in on the accurate notes during the duration of the note. Though she none of this can be indicated in the music notation and has to be decided on by the performer, normally not randomly, but to match an agreed style of performance. So all of this can happen during one note of one instrument of the string quartet, never mind the other 5000 notes in the piece of music!
And then there's the transition from one node to another. The transition is not indicated all, other than perhaps by a phrasing mark above the bars. The starting point and its ultimate end are symbolised by 2 successive notes. What happens between is almost never defined, (utmost bite indication of the slide, but this is rare). But a violinist will make use fairly continuously of small slice between notes, not sufficiently obvious to constitute real portamentos, but nevertheless very significant in the musical performance. These vital and unwritten no transitions are a matter of style, and only the best musicians can perform them effectively.
Singers also "scoop" audibly to and from every note of Legato passage. They are traditional only. Some years ago I heard a Russian singing group in a local church. The Sopranos saying a version of Ave Maria that sounded quite extraordinary in the way that notes were slid together and crescendos and diminuendos appeared through and between notes. It was style of performance that totally amazed the English audience, but it was just a style that wasn't written in any school. This is part of the living language of music.
As explained, notation is really a convention that indicates the general proportions and flow of a composition, but it is only a rough guide. You can consider it as a blueprint around which to construct the performance. The further away from classical Western music you get, the more vague and fuzzy this blueprint is. When I was first taught the violin, online music sources like Spotifiy didn't exist. Violin lessons were about a teacher guiding you on how to improve, and you listening to yourself and trying to interpret what sound you are playing. What you heard was never what your teacher heard, so their long discussions and indications about how the performance could be changed, during which there were 2 views of the process. I remember preparing for the University music competition, with the help of a tape recorder. I'd had lessons on the piece of music that I was going to perform, but what it did it really sound like, in truth I had little idea. So I did something which was quite unusual for that period, I got a recording of Yehudi Menuhin playing the piece, (on the basis that he wasn't bad at all at playing the fiddle), and importantly he played the piece in a way that I liked and meant something to me. I then recorded myself playing and compares my recorded performance with his. It was a shock to say the least. It was much more unkind and illuminating in a conventional violin lesson. I made changes that I thought would make it sound more like Mr Menuhin, some of which move the music in the required direction and some of which were way off course. But because I was able to hear it as other people in the audience would hear the music, it was very informative. (It must have worked as I did very well in the competition).
How things have changed. Not only can one do audio recording, but one can easily do video recording to see how the mechanics of playing, (and playing a violin, or for that matter any instrument, is a complex mechanical undertaking. Humans are merely machines, and very complex machines at that.) One can record the whole string quartet on video, or ceilidh band or jazz band, whatever type of music it is that your reminiscing. Not only can you hear what isn't right, you can often see physically why the right sound is not coming out, and one can change one's physical and mechanical technique as the first step to improvement.