Monday, April 8, 2013

Comb Filtering

(I'm writing this article as part of the Introduction to Music Production course on Coursera.)

Comb filtering is an interesting phenomenon. When you play audio back with itself at a very slight delay, it causes interference patterns. Most often, this occurs when a reflective surface is near your microphone.

In my studio, I took a speaker and played white noise from my computer through it. Then, I placed a microphone near the speaker, and sent that audio back into the computer. I used the channel EQ plugin to look at the frequency response of the audio after it went back into the microphone.

Then, I took a reflective surface (a dry erase board, in my case) and gradually brought it closer and closer to the microphone and speaker. As the board gets closer, it takes an increasingly shorter time for the sound to bounce off the surface and get to the microphone. As the delay gets shorter, we can start to hear the filter effect more and more.

If you watch the frequency response displayed on the screen, you'll see notches and peaks begin to appear at regular intervals. This is where comb filtering gets its name, because the frequency response looks something like a comb!

Monday, April 1, 2013

How dynamic processors work

(I'm writing this article as part of the Introduction to Music Production course on Coursera.)

In my last blog article, I mentioned dynamic effects as one of the main categories of plugins, and explained that they function as a sort of automatic volume control. Today, we'll look at the four main working parts of dynamics processors: threshold, ratio, attack, and release.

The threshold setting describes when the plugin kicks in. It is usually given in dB units. In a downward compressor, when the audio signal reaches the threshold, the compressor begins reducing the signal's gain.

The black curve represents the original audio
signal, and the red line represents the threshold.
The ratio setting describes how much the sound is modified. A 2:1 compression will reduce the signal above the threshold by half. This means that if the input signal is 2 dB over the threshold, the compressor will reduce it to 1dB over the threshold.

The blue curve represents the compressed
audio,  reduced by a ratio of 2:1.
The attack and release parameters control how quickly the plugin reacts. In a downward compressor, the attack is how long it takes for the compressor to start reducing gain after the threshold is reached, and the release is how long it takes for the compressor to stop reducing the gain once the signal drops below the threshold.

Compressors, limiters, expanders, and gates all have these four parameters. Limiters function very similarly to compressors, but have extremely high ratios. Basically, they never allow the audio signal to get more than a little bit above the threshold. Expanders are sort of like the opposite of compressors. The reduce the signal when it drops below the threshold, which increases the dynamic range, making quiet signals quieter. Gates are basically extreme expanders. Whenever a signal drops below the threshold, the gate will allow no signal through.

Monday, March 25, 2013

Basic types of audio effects plugins

(I'm writing this article as part of the Introduction to Music Production course on Coursera.)

In a digital audio workstation (like Logic, Reason, Pro Tools, etc.), there are many different audio effects that can be applied to tracks. These effects can change sound in almost any way, and there are countless plugins to choose from! Today, we're going to take a look at three of the main categories: dynamic, delay, and filter effects.

Dynamic plugins affect the amplitude of a sound. Basically, they function like automatic volume control. This includes compressors, limiters, expanders, and gates, among others. This is what the "Compressor" plugin in Logic looks like:

Compressors are used to reduce the volume of the loudest parts of a track.

Delay effects have to do with the propagation of sound. They play slightly modified sounds back at a slight delay, which can have a variety of effects, like simulating the sound in different physical spaces. Delay effects include plugins like reverbs, delays, phasers, flangers, and choruses. This is "Space Designer," one of the reverb plugins in Logic:

Sunday, March 10, 2013

Recording signal flow

(I'm writing this article as part of the Introduction to Music Production course on Coursera.)

Let me give you a rough overview of what happens every time I hit my snare in my studio.

My brain generates a signal. It starts in the motor cortex, racing across each neuron as an action potential, and crossing each synapse by the release of specific neurotransmitters. It travels through the thalamus, then down my spinal cord. It goes to nerves in my arm, contracting muscles, which in turn flex and extend my joints. Starting from my shoulder, a whiplike motion occurs. It moves through my arm, elbow, wrist and then fingers, exerting force on the drumstick in my hand. The drumstick accelerates downward, making contact with the batter head of my snare:

When the drumhead begins oscillating, it alternates between compressing and rarefying the atmosphere, creating longitudinal waves of sound pressure variation. These sound waves travel through the air and make contact with the diaphragm of this Audio Technica M4000S dynamic microphone:

Monday, February 11, 2013

How to play the groove from Liquid Fire by Gojira

This is a sweet groove from the song "Liquid Fire" by Gojira, on their album L'Enfant Suavage:

The idea here is fairly simple, but somewhat difficult to execute. The hands merely are a 16th note paradiddle. The right hand is on the bell of the ride, and the left hand is on the snare. Every time the left hand starts a paradiddle, it is played as a rimshot, and the rest are played as ghost notes.

The tricky part is the foot pattern! The feet are playing a grouping in 5/16; three consecutive 16th notes, followed by an 8th note rest. This pattern in 5/16 doesn't line up with the quarter note. In fact, it takes five quarter notes to line back up.

The problem is that the paradiddle doesn't line up evenly with those five quarter notes. After five beats, the paradiddle will be starting on the left hand. It then will be another five beats before the foot pattern and quarter note lines up again! However, this time the paradiddles, quarter note, AND foot pattern will all be in sync.

It makes more sense if you think about all of them in terms of 16th notes. A quarter note is four 16th notes long (1e+a), the foot pattern is five 16th notes long (XXX - -), and the paradiddle is eight 16th notes long (RLRRLRLL). So we're dealing with three different groups of 16th notes, 4, 5, and 8. What we need to understand is how they all line up.

The paradiddles and quarter notes line up easily; 4 fits evenly twice into 8, so the paradiddle lines up with every other quarter note. The foot pattern is not so simple, since 4 does not fit evenly into 5. We need to find the least common multiple of 4 and 5, which is 20. That is fine, but we have new problem. Our paradiddle, which has 8 notes, does not fit evenly into the 20! This means that when the 5 and 4 line up, we will be halfway through the paradiddle. Now, we need to find the least common multiple of 4, 5, and 8, which is 40. So, in the space of 40 16th notes (which is 10 quarter notes) we can evenly fit the 8 note paradiddle, 5 note foot pattern, and the quarter note pulse. That is the full length of the pattern, before it repeats!

Wednesday, February 6, 2013

How to improve your double stroke roll

One of the most important exercises that I have used over the years to develop my double stroke roll is playing through all of its inversions. If you aren't familiar with the concept of inversion of rhythms and rudiments, it's actually quite simple. All we're doing is starting on a different note! The double stroke roll has four notes before it repeats, so we should get four different variations.

The normal double stroke roll looks like this:

If we start on the second note, we get this:

Now the third:

And the fourth:

That gives us all possible inversions the double stroke roll. Now, let's take all four of these patterns, loop them, and put them back to back. If you'll notice, each inversion ends on the hand opposite of the start of the next inversion. This allows us to switch fluidly between each one without stopping:


This exercise will tend to force you to play your double strokes evenly from hand to hand, as well as play the second note of each double as loud as the first. If you spend a few minutes every day with it, you are certain to see some improvements. Make sure to use a metronome, and keep everything honest and clean! Bonus points if you play these with your feet as well as your hands ;)