Learning goals
- Learn about pitches, frequencies, and scales
- Add melodic parts to a composition
What to do
The goal for today is to start to add melodic parts to the composition you started in Lab 5.
Pitches and scales
Here is a tiny bit of music theory.
Octaves
A note’s pitch is determined by its frequency. The higher the frequency, the higher the pitch.
An interesting auditory phenomenon occurs when you multiply a note’s frequency by 2: you get a higher note that sounds “the same” as the first note, only higher:
Frequencies that differ by a factor of 2 are one octave apart.
So, what about notes within an octave? Western music uses a 12 tone scale, meaning that there are 12 distinct pitches in each octave. The difference between two notes is called a semitone or a half step. So, what is the relationship between the notes within an octave?
The basic idea is that we want the notes within the scale to be separated by more or less the same difference in pitch. Because the next higher octave involves doubling the frequency, moving to the next note involves “one-twelfth doubling” of the frequency. The idea is that there is a factor, which, if multiplied by a note frequency, gives us the frequency of the next note, and, if we multiply a note frequency by the factor 12 times, we effectively double the frequency, giving us the same note at the next higher octave.
This “note multiplier”, which we’ll call f, can be computed as
f = 21/12
In other words, 2 raised to the power 1/12. This factor is approximately 1.059. Multiplying any note frequency by f gives us the frequency of the next higher note, and dividing by f gives us the frequency of the next lower note. This scheme is known as equal temperament, and in modern times is used nearly universally for instrument tuning.
Note that because equal temperament only tells us how to move between notes, we need to have one note’s frequency to be specified as a constant. The most common standard is that A4 (the note “A” in the fourth audible octave) is defined as exactly 440 Hz. All other note frequencies are defined relative to this reference point.
Scales
If you’ve ever sat down at a piano or keyboard and played random keys, you’ve probably noticed that it doesn’t sound very good. This is because most western music uses notes selected from a scale. Typically, a scale includes exactly 7 notes (and variations in lower and higher octaves). Scales are defined by specifying a pattern of how many semitones there are between notes, starting at the root note of the scale. The important thing to realize about scales is that the number of semitones to reach the next note is not always 1!
A major scale uses the following pattern of semitones:
2, 2, 1, 2, 2, 2, 1
Here is a C major scale:
A natural minor scale uses the following pattern of semitones:
2, 1, 2, 2, 1, 2, 2
Note how in each case, the sum of the semitone increments is 12, which makes sense, because the progression specifies how to reach the scale’s root note in the next higher octave.
Here is a C minor scale:
Notice how the major scale sounds “happy”, and the minor scale sounds “sad”.
What this means to you
You will probably want to pick a scale to use in your composition, and use notes selected from that scale. In particular, C major and A minor are good choices, because the notes in those scales correspond exactly to the white keys on the piano keyboard.
Example: Thieves Like Us
Lab 5 included a small fragment of New Order’s Thieves Like Us as an example of percussion and bass.
Here is the code we started from:
We’ll continue this composition by adding melodic instruments and figures. Thieves Like Us is a good example of 1980s dance music: 4/4 time signature, lots of syncopation in the rhythm parts, moderate tempo, repetition of simple melodic figures with a good bit of variation as the piece progresses.
Here is a link to the enhanced version:
Let’s analyze what we added.
Synth #1
Our original version had a break of 4 measures with just bass drum and snare. This is actually supposed to be 8 measures, and it includes an iconic synth lead.
We’ll start by creating an instrument, using patch 91 (“Pad 3 (polysynth)”) in the FLUID
soundfont:
Synth “pads” generally have a “full” sound, and may sound like multiple instruments.
We define the following rhythm, melodies, and figures:
Notice that there is a single rhythm which is played using three distinct melodies to create three distinct figures.
We incorporate these figures into the break as follows:
Synth #2
The second synth part is sort of a staccato background part that comes in behind the pad part. I used FLUID
with the Harpsichord patch (7):
Note that a few audio effects are added to the instrument, specifically delay (echo) and reverb.
Here are the rhythms, melodies, and figures:
These are played in pairs: synth1f
is followed by either synth2f
or synth3f
. These figures are played along with the existing kick drum, snare, and hihat parts:
Fifths lead and guitar!
After the synth parts, there are 8 measures where a “fifths” lead alternates with distorted guitar chords.
Instruments:
Rhythms, melodies, and figures:
Note that the start beat in the guitar rhythms is negative — the guitar figures start early (just at the end of the previous measure.)
These figures are played with the original kick drum patterns, a new snare pattern, and the original bass pattern:
Putting it all together
It sounds like this:
Your turn
Add some melodic parts to the composition you started in Lab 5.
Suggestion: once you have rhythm and bass parts you are satisified with, try adding a synth pad to your composition.