Though Sound and Rhythm are integrated, we may separate the two, and study their individual function in music.
Likewise, different instruments usually overlap each others' roles in a song. However, we may separate their parts into highs and lows within these basic Parts of Sound:
(I added percussion, since it produces tones in the different parts of sound). Not only bass and percussion, but any instrument automatically supports rhythm, with short/long tones, and loud/soft dynamics and phrases. We can hear that even melodic sound contains duration and time, that marks out rhythm.
Loudness or quietness can be gradual, such as at the beginning of a phrase, and then at the end of a song. A gradual loudness, or 'fade-in', is called a Crescendo. Press the pics to listen.
A gradual quietness, or 'fade', is called a Decrescendo.
Louds and softs help to understand where a musical 'conversation' begins and ends.
Dynamics of sound also mark Rhythmical changes. With any good song, there's a build toward a climax, which is usually the loudest, and most dramatic part of the song. Then the anti-climax part, leading to the end, begins to quiet down, and sometimes even slows down. Bands like to 'fade' the sound near the end, on recordings. They simulate this effect, when live, by playing slower and softer. It's like a bird landing.
As you play, be aware of where you are, in this musical 'storyline'. Also, if you are playing harmony, you are actually playing your own melody that is a 3rd, 5th, or some other step away from the main melody. Your melody complements the high part that's speaking the sentiment of the song.
When playing the bass part, you carry the melody, harmony, and rhythm as well, definitely complementing the whole song. 'Speak' to the other members, to create an overall thought for which the song is written (interpretation). Notes, when played at the same tuning, loudness, and duration, will present the chords as one. This cooperation between rhythm and tones glues together the song, no matter how many people are playing.
A note does have a tone and a length, but its sound doesn't have to be boring!
Vibrato, which sounds like 'vibration', helps the note to move up and down quickly, and closely to the note itself. You're not really moving the note a half step up or down (wouldn't that be another note anyway?), but you're finely 'swelling' the note.
Vibrato can start quickly and end slowly, and sounds good with a Decrescendo at the end. You'll quickly pulsate the note according to the rhythm, and according to the phrase. If you sing a note, saying, 'ya ya ya...' many times, it will sound like vibrato. String players frequently employ vibrato .
A Trill is like a vibrato on crack.
You actually change notes quickly, with attending dynamics and length. Play a note, go up to another note, go back to your first note, go up again, and do this many times very quickly. Practicing this will make it sound smooth. If you whistle two notes many times as quickly as possible, it will sound like a trill.
A Turn is like a trill, but has more notes (it can also be called a mordent).
You start on a note, go up to another note, come back to the first note, go down a note, then land on the first note. Really, you are playing one note, but adding an upper and lower 'flip' from that note. You can do this as quickly as you like, with the 'beat' in mind. It's usually a lead into another note.
Grace Notes are important, because most music that sounds professional uses them. You think about playing a note, but before you play it, you quickly preceed it with a (usually) lower note. It's like a 'pickup' note. Really, it's so quick (and graceful), that it sounds like one note. Do this to emphasize notes, and generally to sound 'cool'. You can use it on the first note of a phrase, or wherever notes are separated.
Orchestras have many grace notes that start higher than the landing note. It's lighter sounding, and is like a tripping sound if many grace notes are connected.
A Glissando is like a fast series of notes, going up or down. This produces the effect of dramatically introducing, or exiting, a tone or phrase. You simply play whatever scale in the key, or chromatic scale, as fast as the tempo will allow, up to the note you want, or down from the note you're on. If you whistle like you're whistling at something sexy, you'll have a glissando going up, and one coming down. You just 'glide' quickly up or down.
A Roll is like a turn, only slower, involving more notes.
You play a small phrase that goes up and down in sound, then repeat that phrase over many times. Usually, this phrase picks up speed the more it's repeated, then slows at the end. So it sort of 'rolls' up and down, or over and over, to the end of the beat. You can use any notes, or number of notes, you choose. It sounds good if they go up and down in sound (or the opposite), pressing the roll foward.
Accents are important to rhythm. They are much louder, or much softer notes. Also, they can be a little longer, or shorter than surrounding notes. A note that's played louder than the others in a phrase, accents it so that note stands out in rhythm. Playing the notes near it softer, makes it stand out more. Likewise, make a note before an accented note closer in time to strengthen the accent.
These subleties in duration and loudness will become apparent by listening. Play a simple phrase, pick out a note, play that note louder than the others, and see how it changes the interpretation of the phrase. Next, lengthen some of the notes together (tenuto, legato), to hear how they flow. Then, shorten certain notes (staccato), to see how they change the phrases' interpretation.
Insert some vibrato, grace notes, turns, trills, glissandi, or rolls in spots that sound like they need it. Maybe another phrase pops into your mind ... and it goes berserk, creating music independently! Yay improvisation!
The next page makes interesting comparisons between types of scales: Major, minor, parallel, relative, and pentatonic.