If you are in France and mention  'enveloppe' and  'timbre' in the same sentence you will be  handed an envelope and a postage stamp.  Say 'merci'  and  go write your letter.  This postage envelope  has nothing to do with the topic of timbre. 

On the other hand...

The  sound envelope  - Attack,  Decay,  Sustain,  Release - is how the intensity  or  strength  of  a  sound  varies  with  time.

The ADSR envelope can create sounds that have an initial  tonguing  sound or click. For example  you might hear the click of the plectrum  on  the string at the start of the note when an acoustic guitar is playing.

The following are three rough diagrams of a piano, a plucked string and a brass/ bowed string envelope.
 
 

Note that in the final extract (violin) that there is a certain amount of vibrato which adds richness and depth to the timbre.
Vibrato = smooth variations in  pitch.  The violinist's fingers (left hand) wobble slightly on the string.
Tremolo = smooth variations in volume. The violinist's bow (right hand) causes this. The word tremolo can also describe a rapid repetition of a note.

Amplitude refers to loudness.  Frequency refers to pitch.  Certain notes need greater effort and pressure on the part of the player.  The  envelopes, especially the attack transients, will be different, if one note is, say, an octave higher than another.

Task 2

Read the following and then fill in the answers on the Revision sheet that your teacher will give you (pdf).

Question

Attack?  Envelope?  What are they doing in a lesson on timbre? 
Haven't we already worked out that the harmonics influence timbre?  Is there more?

ADSR = Attack - Decay - Sustain - Release

There is an initial attack where the sound builds up to its maximum intensity. The level then decays or fades until it reaches the correct level for it to be sustained and finally it is released when the note falls away to silence.
 

A drum beat has a percussive envelope and,  like a plucked string, it will have an almost instant decay.  The sound is not sustained or released.  For a wind instrument the decay  can be quite long.

When a sound builds up to a certain level and stays there until something else occurs this constant level is called SUSTAIN. A bowed envelope has a slow attack (unlike in this diagram)  followed by a long sustain and then a slightly  faster release.  There is no decay between the attack and the sustain stages.

The decay rate of a sound will vary according to whether or not damping is applied. When you strike a key on a piano,  the rate at which it dies away depends on whether or not you stop pressing the key. If you hold it down, the sound dies away slowly whereas if you release it the sound dies away more quickly. This stage of the envelope is called RELEASE .

As well as the general envelope described here there is also a timbre envelope.
The quality of a note changes as the sound decays. The harmonics which give the note its characteristic quality or timbre die away at different rates. This change in the sound quality as the note ages is called the timbre envelope.
So each sound has a volume envelope and a timbre envelope.  The shape of a piano envelope while playing a note is different from that of an organ or trumpet or banjo or viola or any other instrument playing the same note.

Task 3

Find out by using real examples how to change the timbre of music
by tampering with the envelope.

Now it's your turn to experiment with timbre.
1  Blown
2  Plucked
3  Bowed
4  Struck

There is a multiple undo facility in Cool Edit Pro so you do not have to keep the new sounds.     Keep listening to the effects.

1. Click on this wav file  
2. Save it to your desktop.
3. Open Cool Edit Pro and open the wav file. It is called    oboeC5.wav and lasts 2 seconds
4. Play it and listen.
5. Go to the Transform menu;
6. In the Amplitude section, try out different Envelopes...then, experiment!
7. Remove the attack;
8. Reverse  the sound;
9. Stretch the sound;
10. Save under different file names, as you wish.
11. Check out the differences in the View menu  by looking at the spectral image

• What transformations bring about the greatest change in the timbre? 
• How can you make it sound like another instrument?
• When you remove the attack, is there enough information in the steady-state portion to allow the listener to recognise the oboe?

Look at the Envelope window below.  This new envelope was applied to the wire.wav

• Click on this wav file  
• Save it to desktop
• Open Cool Edit Pro and open this file.  It is called wire.wav

Try out the other envelopes - create your own envelope.
Notice that you can preview the new sound each time.  No need to save.
 Look at how the waveform is altered when this envelope is applied. This happens to be a stereo wav.

The piano is really  a large iron harp with steel strings  in a wooden box with soundboard.  The felt-covered hammers  strike wire strings and the sounds  may be softened or sustained by using pedals. In grand pianos  the harp is horizontal.  In an upright piano, the harp is vertical.