In music theory, the key of a piece is a group of notes that corresponds to a certain musical scale that forms the foundation of a music composition.
A musical key is the home of a music composition. It features a tonic note and/or chord its corresponding notes and/or chords. The tonic note or chord provides a sense of arrival and rest. It has a unique relationship with the other notes or their corresponding chords. Notes and chords other than the tonic create various degrees of tensions and those tensions resolve when the music returns to the tonic note or chord. This is how music works.
Keys and Scales
In tonal music, a piece can either be in major or minor key. However, some longer pieces in the classical repertoire may have sections in contrasting keys.
The key of a piece of music is related to a musical scale. For example, if a piece is in C, it is primarily based on the C major scale. Mostly, it uses the notes of that particular scale for its both melody and harmony. So it uses the seven notes of the C major scale – C, D, E, F, G, A, and B. If a piece is in C minor key, it is primarily based on the C minor scale. It mostly uses the notes of the C minor scale. Those notes can be from natural, harmonic and melodic minor scales.
In tonal music, the tonic note is like the gravitational center. It is the most important element of music. So the tonic note of the key acts as the center of the key. For example, the tonic note of the F major scale is F. When we listen to a music in the key of F, we realize that the music is constantly being pulled toward F. So the tonal music usually revolves around the tonic note.
We can say that the tonic note is like a final resting point too. If a section of a music ends with a note other than the tonic, it feels like it doesn’t end yet. When we move away from the tonic note, we create a sense of tension. This tension wants to resolve or to come to a state of rest or conclusion. It wants to reach the tonic note or chord. We can provide that resolution by bringing the music to the tonic note or chord.
An exception to this though is atonal music. When a piece of music lacks a tonal center, we call it an atonal music.
Establishing The Key Of A Particular Piece
The idea of a musical key may be confusing in the beginning. Because a piece of music can actually use the notes other than the corresponding scales. For example, we can use a Dorian mode in a piece of music in a minor key. Then how do we establish the key of a particular piece? There are several ways of establishing a key of a particular piece.
Using Key Signature
You have learned about key signatures in major and minor scales. A key signature is a set of sharps or flats placed together on a musical staff. We place key signatures right after the clef, before the time signature. If we have the sheet for a particular piece of music, we can usually establish its key by looking its key signature and its notes.
The notes and chords of a piece in a particular key are usually in the corresponding scale. This way the music orients the listener around the tonic note. The key signature of that piece can give us a valuable information of which major key or its relative minor the music is written in. Let’s see an example.
This is the same example we have given in the modes subject. As you can see, there is only a flat on B in the key signature. This means that this music is either in F major or in D minor keys. So how do we discriminate between a major key and its relative minor? Because we have two choices here. Apparently, the key signature is not reliable alone to establish the key. We should also look for the notes of the piece. It starts and ends with F. It sounds like the note F is of greater importance. Also, it sounds like it is written on a major scale. So we can easily say that this music is in the key of F.
Listening for the Tonic
When we don’t have the sheet of a music, of course, the best way of establishing the key of a music is listening to it. We should try to pay attention to the tonic notes or chords. We also try to find the sections where the music resolves. In fact, most tonal music finish on the tonic of the key for making them sound finished, resolved or in rest. When you listen to a music carefully, you establish the point where it sounds like resolved or unresolved. Finding the tonic note or chord is usually also finding the key of music.
Listening to the Mood of Music
The mood of a music doesn’t give us the exact key of a particular music. But it gives us a clue about if the music is in a major or minor key. Major keys are considered to have a happy mood while minor keys have a sad, melancholic or romantic mood.
In an ideal world, a piece of music in a particular key usually uses the notes of the corresponding scales. But there are exceptions to this. We don’t always have to use the notes on a scale. We can use other notes too. But usually, the bulk of the notes will still revolve around that particular scale. If a piece of music is composed properly, these outside notes don’t prevent us to establish the key of that piece. If they are used improperly though, it is almost impossible to establish the key of that piece. Again, we can figure out this by listening. Because it creates an unpleasant effect. However, in some genres like jazz, musicians and composers use a lot of outside notes in their solos.
Transposing Instruments and Concert Pitch
Written middle C of some instruments produces pitches other than middle C. Those instruments are referred to as transposing instruments. For example, when we play a music which is written in C major key on a B flat clarinet, it sounds in B flat major key. The written C will sound as B flat. So the notes sound a major second lower than they are written. This is why when we write music for transposing instruments, we should consider the difference between a “written” and “sounding” notes. In other words, the concept of transposing instruments is nothing more than a notating convention. When we write music for transposing instruments, we transpose, or in other words, we change the pitch of transposing instruments into different keys from that of non-transposing instruments.
Concert pitch is the pitch reference to which musical instruments are tuned for a performance. It is also known as international standard pitch. The most common tuning standard uses 440 Hz for A above middle C as a reference note. We set other notes relative to it. We also use the term “concert pitch” to distinguish between the “written” and “sounding” notes of a transposing instrument. So the concert pitch is the pitch on a non-transposing instrument as on common C instruments. In other words, when we play a music which is written in C major key on a common C instrument, it sounds in C major key. Because the written C sounds C on a non-transposing instrument. So when we write music for them, we don’t have to change anything.
Transposing instruments are mostly found in C, E flat, F, and B flat. Here is a list of common C instruments and transposing instruments.
Common C Instruments
- Contrabass (Double bass)
B Flat Instruments
- Bass Clarinet
- Soprano Saxophone
- Tenor Saxophone
- French Horn
- English Horn
E flat Instruments
- E flat Soprano Clarinet
- Alto Saxophone
- Baritone Saxophone
There are some other transposing instruments too. For example, D flat, D, G and A. The same logic applies to them.
Here is a table that shows “written” and “sounding” notes of common transposing instruments.
Up Major 2nd
Down Major 2nd
Up Perfect 5th
Down Perfect 5th
Up Major 6th
Down Major 6th
How do we use this table? When we write a music for a B flat instrument, we write it a major 2nd higher. However, when we play it on an actual B flat instrument, it will sound a major 2nd lower.
Note that for some instruments there may be exceptions. For example on E flat Alto Sax, written C will sound E flat (Major 6th lower). However, on E flat Baritone Saxophone, written C will sound E flat an octave lower (Major 6th+Octave lower).