In music notation specifically for the guitar, there are often picking symbols meaning to pick up or down. What is the purpose of these picking indicators (sorry, don't know the real term for them)? Do they change the sound of the music? To be honest, I usually ignore them, but just now I've been wondering what they really do to change the music (if at all).
To be honest - I think you may be fine just ignoring them as you have been doing. I usually do.
First let's talk a bit about music notation for guitar. In my experience, most music notation for guitar written for Rock, Classic Rock, Pop, Country, Folk (and many other types of popular music that is not strictly instrumental) is nothing more than someones representation of how they suggest playing the song to sound as authentic as possible. In other words - someones interpretation.
On the other hand notation for classical music or music that is strictly instrumental - is very detailed and strict and in that case, the picking patterns would be what the composer intended for you to play. But most classical and many instrumental only arrangements are meant to be played finger-style with fingers and thumb so the type picking pattern arrows you refer to would not be present.
The original artists on most Rock, Pop, Country etc. songs, often play the guitar part different each time they play it (particularly live) and the notation you will find is usually written by someone who listened to a recording of the song and tried to figure out as best they could how to play it so it would sound like the record. Even session guitarist who play in the studio when the record is being cut, will usually just improvise their guitar part on the fly and may play it slightly differently on each take and the producer or artist will just select the one they like best and that's what ends up on the record. But then the artist or guitarist may never play it exactly the same way again.
Often adaptations are made for solo guitar that might even incorporate the bass line or a horn or other instrument - that is prominent in the recording. For example when I play "The Joker" By Steve Miller Band, if I don't have a bass player with me, I play mostly the bass line on my guitar - not the guitar part. Otherwise it would not sound anything close to what people are used to hearing when they hear that song.
So the picking patterns noted - are just a suggestion based on what the interpreter (person writing the notation) feels will be easiest to play and/or best recreates the way the song sounds on whatever recording of that song they based their interpretation on.
If the arrows are on tab or individual note notation for playing a guitar solo, or lead line or riff, then the picking patterns that are suggested are based on what is deemed to be easiest to do considering where the next note will be played (the string below or above) and what happens after that. But you may find it easier to use a different picking pattern. So you should experiment.
If I am looking at tab to try to learn a riff or solo - and there are picking notations (arrows), I will try it the suggested way, but will also experiment with other picking patterns and ultimately decide what works best for me.
It is unlikely that the picking pattern (up-down) notation is intended to create a particular tone or quality to the sound (as would a palm mute notation). When playing individual notes on guitar with a pick, there are many variables besides picking direction that will have more impact on the tone or sound of the note than whether you are picking up or down.
The way you attack the string, the angle you hold the pick, how deep you insert the pick, the material the pick is made of, the thickness of the pick, and other variables will have a greater effect on the sound than whether the pick is moving towards the floor or ceiling at the time it strikes the string.
If playing double stops or power chords (two strings at a time) the picking direction WILL effect the sound as it will either accent the higher or lower string - so in this case, it can be just as important to the sound as it is what is easiest to play.
If the up and down arrows are for chords, it denotes the suggested strumming pattern and will in fact make a difference in the way the song sounds rhythmically as well as the the sound of the chord. When playing a chord on guitar - you are strumming anywhere from four to six strings. Unlike a piano or other type keyboard, you can't play them simultaneously. Thus up-strums will emphasize the treble strings more and down-strums will emphasize the bass strings. Also- up strums are usually a bit softer sounding and don't always include all the strings that would be played on a down-strum of the same chord.
When playing rhythm guitar (mostly chords) as opposed to lead (mostly picking), the strumming pattern is very important. It will allow the strumming to synchronize with the singing and other instrumental parts in a manner similar to that heard on the recording.
But even with strumming patterns- there still may be alternatives that will produce a rhythm pattern that works for the song. I rarely pay attention to someones suggested strumming pattern personally - but instead I just listen to a recording of the song that I want to emulate, and try to re-create the rhythm pattern I hear and feel. But many folks find it easier to follow the strumming pattern notation (arrows) to learn the song.
If you feel that you are playing the songs in a manner that sounds authentic - and the singer and other musicians can follow along - without strict adherence to someone else's SUGGESTED picking or strumming pattern, then I think you are fine continuing to ignore those little arrows and just do what is sounds good and is comfortable for you.
Hope that helps. Rock on.
After thinking and re-thinking... Yes the way you pick does change the music, Imagine in metal all down strokes for rhythm, it does give a different effect than up down up down. Sweep picking, crossing more than one string with the pick all down strokes or up strokes DOES change the way it sounds, playing with fingers changes the sound as well everything gives a different feeling sometimes subtle and other times strong.
In classical music which I used to read sheet music a lot, it was more about making it easy for the player to play the song. But I guess it also had to do with tone as well.
So maybe the actual reason for it is to get you as closer as it can get to the way the song sounds?
Personally I still think that the main reason is about technique and make it easier for the player to play something. And by following the sheet's indications you get good habits because most of the time... They do it the right way.
There's typically an ever so slight difference in the way something sounds when you play a down stroke vs. an up stroke. Down strokes tend to be slightly more accented while up strokes tend to be slightly weaker.
Also in the context of playing chords, playing a chord using a down stroke puts slightly more emphasis on the lower notes of a chord while the up stroke puts more emphasis on the higher notes of a chord. There are some songs where guitars only play up strokes for the effect of it on chords (like Roxanne by The Police).
If you're just using the alternate picking technique this difference will not be noticeable most of the time as it's just to keep time better. I suggest play some riff you play all the time only with down strokes, only with up strokes, and then alternate between them. It won't be drastically different, but it should give you an idea of a difference between the two.
Many of us guitarists hear and feel a real and distinct difference in the sound between an upward pick and a downward pick, be it a single string or full chords. This difference can be important to us as performers. Often the audience only gains a small flavor or sense of atmosphere that is difficult for them to recognize as a type of pick stroke.
Sometimes picking notation indicates style. All down strokes, for example, could indicate a driving style such as punk, or heavy metal.
Sometimes picking markings can convey an easy approach to a difficult patern. "Rake upwards here and then stroke down on this string and up on this one to set up the next downward rake."
Picking down usually has a more solid tone, volume and even rhythm as guitarists often are more comfortable moving in this direction. Up strokes are not the opposite of this, but merely a little less than exactly as comfortable, solid and reliable as a down stroke.
When playing chords often the first string, your strike can be stronger in tone and volume than the last in either picking direction. Also the progress of the pick across the strings is not instant, so you actually hear the strings played one at a time very quickly. This will result in a slightly different sound when you move in one direction vs another.
Strumming patterns can also help guide the rhythm by keeping your arm moving with a particular pendulum like motion. This is a positive thing.
To summarize, sometimes this difference in sound can matter to the listener, but often the more important thing is how it feels when you are playing it.
Picking is as important a skill as left hand fingering, and frankly one that many modern guitarists ignore. The value of the picking marks is somewhat determined by the nature of the music you are looking at. A good beginner music series for guitar will literally teach picking methods and techniques by going through multiple variants of the same song with different fingerings and picking directions. After some practice you should be able to evaluate a piece and choose the best pattern for that piece. Mel Bay's series starts all down stroke for simple songs, goes through alternate picking, and eventually consecutive picking.
Consecutive picking is often heralded as being a "superior" technique by shredders in all genres. It is valuable but with practice one can achieve comparable speeds with alternate picking. At this point it becomes a matter of style for the guitarist. Different picking sequences on the same run (scale, arpeggio, melody line, etc) will produce different tone and feel. So consecutive picking is not just a speed picking technique, it usually produces a flowing legato (connected) sound. Whereas strict alternate picking usually produces a separated, staccato, sound. These relations between consecutive and legato, and alternate and staccato, are largely subjective in my opinion. It has been my experience that with practice one can produce staccato consecutive picking and legato alternate picking.
There is a lot going on with the right hand and it deserves attention. If you are looking at an exercise book then the author wants you to practice a specific right hand sequence. If it's a performance piece then the directions are likely included as a courtesy by the composer/arranger to offer what they think is the best way to play it.
I disagree that it doesn't mater but it is really a mater of choice for the experienced guitarist. Many guitarists pick a picking method and start becoming orthodox practitioners. I am not an advocate of that. I practice, and encourage my students to practice, every possible picking sequence. This is mainly to train their mind body connection and improves control over your right hand. As for which sequence to use when, that is also a mater of taste but as pointed different picking sequences can make a run easier or more difficult, and the different attack will typically cause a different tone. These are points to consider when making the choice.