Lesson 3: Tone Territories.



Lack of clarity is often attributed to insufficient volume, but increasing the volume can sometimes increase the problem. The solution usually comes back to two areas.

The first relates to the shape of the sound wave each instrument makes. If you made individual recordings of a flute, trumpet, sax and violin, all playing a note of the same pitch it would be easy to tell them apart, firstly because of the "envelope" of the instrument, and secondly because of the "harmonic" content.

The envelope is referring to whether the sound starts with a strong burst or with a gradual increase. Violins and flutes have a soft "attack", whereas trumpets, guitars, and of course drums, have a hard attack. This is one characteristic whereby we are able to identify an instrument by just hearing it. Harmonics are sounds that are multiples of the fundamental frequency. If a plucked string vibrates at 100 cycles per second then the harmonics would be 200, 300, 400 etc. The shape of the wave depends on which harmonics are present, in what amounts, and what are their phase relationships. Sine Wave

The simplest wave that appears in nature is the "sine" wave. It happens every time a pendulum swings, and every time a wheel turns.The other common shapes are the square wave, triangle wave, and sawtooth wave. A flute produces a sine wave as the air inside the tube swirls around inside the tube, a sax or clarinet produces a suare wave by reason of the reed slapping back and forth, and the violin produces a sawtooth as the bow stretches the string away from its rest position until finally the tension overcomes the friction and it returns to it's starting position, and the process is repeated thousands of times per second.

Now, lets look at the different wave shapes from a another angle. If we start with a sine wave at a certain frequency (for example, lets call it "f") and add to it another sine wave at twice the frequency (2 x f, or 2f), look at the graph f1+2 below to see what the shape of the resulting wave is. Now lets add another wave at frequency 3f, and another at 4f etc. It can be seen that by adding different combinations of harmonics, the basic outline of some of the other waveshapes can be seen, and its true, if you begin with a sine wave and add certain harmonics a perfect square wave can be created,Other wave shapes whereas if you add a different combination of harmonics a sawtooth is produced, and if you add a different combination again a triangle wave is formed. As the higher harmonics are added the lines of the wave shapes become straighter and corners become sharper. In fact, this is great in the labratory, but in the real world the harmonic combinations are not as clear cut as that, which leads to more irregular wave shapes such as f1+3+4+6 shown below.

Harmonic Content


Now, why is all this science and mathematics important to us as musicians and sound techs? The answer is the same answer about why turning up the microphone doesn't always make the vocals easier to understand, or why the guitar and piano are fighting each other to be heard above each other. The treble control on your mixers, amplifiers, instruments, etc, is in fact a volume control for the upper harmonics. By turning the high frequencies progressively down you are gradually changing the shape of the wave into its simplest building block... the basic sine wave at the fundamental frequency. That vocal that can not be understood might be fixed by simply adding a little treble, instead of raising the overall volume. Never under-estimate the importance of a clear and wide ranging top end in your sound system.

Finally, do you remember at the top of the page I said that there are 2 reasons why your sound might be unclear? The second reason has to do with the acoustics of the room where you are playing. There are 2 types of sound: direct and reflected. Direct sound comes directly from the source to your ears. Reflected sound bounces off every surface in the room.The floor, walls, ceiling, furniture... everything. Some things reflect better than others. These reflections don't necessarily come ditectly to you. Sometimes it can bounce around the room many times before it gets to you. This effect is naturally occurring echo, and in a room where there are many echos it all blends into one mass of sound referred to as reverberation or "Room Energy".

This mass of sound tends to be a similar level throughout the room. Direct sound, however, is strongest near the source, and gets weaker as you move away from the source. Now here is the important statement: Direct sound is clear and intelligible, whereas room energy is muffled and difficult to understand.If you can't understand the words that are being spoken, or the instruments sound like a jumbled mass,it could be because you are hearing more room energy, than direct sound. Turning up the volume does not fix the problem, because it also raises the volume of the room energy.

The solution is to separate the direct sound from the room energy. Here are a couple of suggestions. To reduce the room energy you could use something to reduce the reflectivity of the surfaces (curtains or tapestries will dampen a wall, carpet will dampen the floor, padded furniture absorbs more sound than unpadded). Of course, if you are performing in somewhere like a bar, or a theatre, you don't have those options, but there is a comforting thought... one of the best sound absorbers is the human body. The more people are in the venue, the less room energy. Well, that works if the people are there to listen to you, and they sit quietly, but most bars are not like that...

One thing you can do in a bar is to get your speakers as high as possible and point them down into the audience. This gets the maximum direct sound to the maximum number of listeners. Another alternative is to get a second or third set of speakers half way into the audience, (but be careful because the sound coming out of the remmote speakers must be delayed to match the direct sound coming from the front of house).

Yes, Getting a good clear sound is a delicate balancing act, and there is no single answer, but just keep in mind, that being heard is not always about who has the biggest amplifier...




We're now ready to move on to the next lesson. Click here to go to the lesson about deciding who plays what and when, or click here to return to the Sound Territories and Mixing index page.