Fundamentals of Sound (pt. 2)_Harmonics

Last time we got into some of the basics of sound, discussing the two main attributes:

Frequency and Amplitude

Today we're going to get a little deeper into this stuff so that we can understand how it relates to the music we make.

Quick recap: last time we learned that frequency is basically dealing with pitch - how high or low a sound is. We measure frequency in cycles per second, or Hertz (Hz). Let's listen to a few tones to calibrate our ears:

So what we were listening to were pure tones. Here is a picture of what a pure 440 Hz tone (aka "Concert A") looks like:
What we have been looking at and listening to so far are what are called sine waves. Sine waves are basically pure tones - nice and smooth and even, no additives or preservatives. But, as with so many things in life, reality is almost never so smooth and even...

Here is what Concert A (aka 44oHz) looks like when played by a grand piano:

Whoa. Lots of stuff going on here. I should point out that this picture is zoomed way out, so we're not seeing the individual waves like we were in the picture of the sine wave. But my point is this: there is a LOT more than just a simple 440Hz sine wave playing when you hit the A key on a piano.

Major point #1: Almost no natural sound contains only one frequency.

You might be asking yourselves then, "What are the other frequencies?"

Short answer: harmonics.

Harmonics are whole number multiples of a specific frequency.

OK, so I just lost about half the class with that last sentence. But it's really not that complicated. Check it out:


So, we're looking at the first 5 harmonics of a vibrating string. The first harmonic is what is called the fundamental frequency. The fundamental is like the "main note" being played. For example, in the picture of the piano note above, 440 Hz is the fundamental, but all that other stuff in the waveform is a bunch of harmonics:

1st harmonic (aka fundamental) = 440Hz
2nd harmonic = 880Hz (440 x 2)
3rd harmonic = 1320 Hz (440 x 3)
4th harmonic = 1760 Hz (440 x 4)
5th harmonic = 2200 Hz (440 x 5)

Every musical instrument has harmonics, but the amounts and combinations of these harmonics are unique to every instrument. This is why a guitar sounds like a guitar, a snare drum like a snare drum, Mariah Carey like Mariah Carey, etc.

Here is a comparison of a flute, a clarinet, an oboe, and a saxophone all playing Middle C (256 Hz):

As you can see, they are similar (they are all instruments from the woodwind family), but it is the unique harmonic content that gives each one a unique sound.

Major Point #2: Even though different instruments (including human voices) have different frequency ranges, most of them overlap.
Here is a chart that shows some instruments and their ranges (click on the picture to see a larger image):

For example, a violin, an MC's voice, and a snare drum may all contain a lot of the same frequencies. This is important to understand when you're mixing music because if you have a bunch of instruments all playing in the same general area of the frequency spectrum, it means that they are all competing for the listener's attention. So, what you want to do is give each one its own special spot in the mix. You do that by cutting certain frequencies and boosting others.

Cutting and boosting- that's the basic concept. Now let's talk about the tools you have to accomplish this. There are basically two types of EQ that you use in mixing:

1. Shelving EQ - This is simple. With a shelving EQ, you're just boosting or cutting everything above or below a specific frequency. This is a more general tool that lets you make adjustments to big sections of your sound. You will generally have one for dealing with the High Frequencies, and one for the Low Frequencies. Here's a chart:
2. Peaking (aka Parametric) EQ - This one let's you zero in on a very specific frequency range to cut/boost. This is a more precise tool for working with really detailed parts of the sound. Generally, you will have a couple of these that are meant to be used in the Low-Mid and Hi-Mid ranges. Here's a chart:


This is what the Digirack EQ plugin that comes with Pro Tools looks like:


Notice that there are five sections of EQ (not including the filters). The middle three sets are all Parametric EQ. The ones on the far left and far right can be EITHER Parametric or Shelving, depending on how you set them. They will normally be set to Shelving.

Really knowing how to EQ is an art form and, just like any other art, takes years of practice to really master. Just remember:

LESS IS MORE. Something that is recorded halfway decently should not need more than a little EQ adjustment. Anything more than +/- 6 dB is a pretty big adjustment.

Fundamentals of Sound (pt. 1)_Frequency & Amplitude

So far we've discussed a bunch of different topics, from music theory to hip hop history to navigating software. Today we're going to talk a little about the science of sound.

What is sound?

On the most basic level, sound is the vibration of molecules. Since we live in an air-filled atmosphere, sound for us is usually the vibration of air molecules.

Whenever there is any kind of impact or friction in our air-filled environment, the air molecules get compressed and are pushed out of their normal positions. They then react by springing back in the other direction. Same concept as a pulling a piece of string tight and then plucking it; the molecules swing back and forth.
When molecules vibrate, they get pushed out of their normal positions and bump into their neighbor molecules. This causes the neighbor molecules to vibrate, and bump into their neighbors, which bump into their neighbors, and so on. These vibrations spread out in all directions in waves, sort of like dropping a rock in a pool of water. This is how the sound gets to your ears. The waves move outward from the sound source at a steady rate, but they get weaker and weaker (quieter and quieter) as they move farther and farther away...

If we try to draw a picture of a sound vibration, we get something like this:
A picture like this is called a waveform. By now, we're all used to seeing waveforms from our recordings in Pro Tools. And as you probably remember from editing, when you zoom in really close, then we see something like this:



What this picture is showing you is one vibration, or cycle. If we think back to the example of the plucked string, this is the equivalent of the string being plucked, then swinging out in the opposite direction, then coming back to its original position. But when you pluck a string, does it just vibrate once and then stop? Of course not! It vibrates many times, but let's keep this idea of cycles in mind as we get to the main topic for today...

FREQUENCY and AMPLITUDE

Here are the basics of what you need to understand:

Frequency = pitch (Hz)

Amplitude = loudness (dB)

Frequency is the number of cycles that happen in one second. The higher the pitch of the sound, the more cycles (aka vibrations) are happening in each second. Therefore, a note played on a high pitched instrument, like a flute, is going to have many more of these cycles in one second than a low pitched instrument, like an 808 bass drum. In the waveform diagram below, the horizontal (left to right) axis is showing frequency. You can see certain sections where the cycles are pressed more tightly together than in other parts. Do you think these parts are lower or higher in pitch compared to the parts where the cycles are spaced out more?The unit of measurement of cycles per second is Hertz (Hz).

Amplitude is the amount of energy that goes into making the sound, i.e. how LOUD the sound is. If I slam my hand down on the table, it makes a much louder sound than if I lightly tapped the table with my finger. This is because I put a lot more energy into making the sound and our ears interpret the amount of energy as loudness. In the waveform diagram, the height of the wave is showing you the amplitude.The unit of measurement of amplitude is the decibel (dB).

Last and thing to know for today:

The human range of hearing is approximately 20Hz to 20,000Hz.

With this information, we can start to get into really working with sound and making it do what we want! (Mwah ha ha!).

Next time, we will get into the wonderful world of harmonics...