Thursday, July 30, 2009

Useful Noise

When you hear people touting the merits of their favorite synth, you're pretty much guaranteed to hear them speaking of the quality of the oscillators or the filters. Almost never will you hear any mention of the noise generator, and that's a shame. Sure, most noise generators sound pretty similar in their raw state, but a noise generator is an incredibly useful thing for sound design, so I thought I'd talk a little about that today.

• 9 times out of 10, when you're talking about a noise generator on a synth, you're really talking about a white noise generator. White Noise is essentially a signal consisting of totally random frequencies that sounds like a steady hiss. There are, however, other 'colors' of noise (and if anyone out there knows how the color naming for types of noise came about, I'd love to hear it...) differentiated by the spectral density of certain frequency bands. Pink noise, for instance, tends to have bit more emphasis on lower frequencies, so it can be useful for synthesizing 'boomy' sounds like kettle drums or explosions. There is also red noise, blue noise, violet noise, grey noise, orange noise, and special definitions such as green noise (supposedly the 'background noise' of the world), and black noise (aka silence). White noise is all you're likely to find on most synths, though (some synths offer pink noise, too, but this is less common). Because most of these other types of noise are based on frequency biases, you can emulate them by boosting the proper frequencies in white noise with an equalizer.

• White noise is very useful for emulating natural sounds such as ocean waves or wind. Just use an envelope or LFO to modulate the cutoff frequency on a low pass filter. A little resonance on the filter can lend a bit more 'howl' to your wind at lower cutoff values.

• Noise is also an essential component in virtually any drum or percussion sound. It's rarely used in kicks (although if it is controlled with a short envelope, it can add a little impact to kick sounds too), but is great for emulating the rattle of a snare drum, the body of hand claps, and hi-hats.

• Speaking of hi-hats, they are dead easy to emulate with a noise generator. Just use a very short amplitude envelope for closed hats, and one with a longer decay for the open hat. Program your hat sounds to be monophonic too, so that the closed hats cut off the 'ring' of the open hat, just like real hats do. If your synth has a high pass filter, try using that and setting your cutoff value rather high. This will get you a slightly more metallic-sounding hat than a low pass filter will. If you want still more metallic-sounding hats, try using a ring modulator.

• Noise is also really useful for all manner of trance whooshes, reverses, and transition effects. Try sending the noise through a filter and automating the cutoff value to generate the whoosh. Experiment with different resonance values on the filter. Add a phase effect to get a cool retro whoosh effect. Throw some stereo delay or reverb on to 'embiggen' the whoosh and create more atmosphere. Sweeps are always good candidates for compression as well. Adding some light compression will even out the levels and make the sweep more audible throughout its entire range in a mix.

• Did you know you can play a melody with noise? Send some noise through a low pass filter with a low cutoff value and high resonance level, and it begins to take on a cool, tonal quality. Getting it precisely tuned across the keyboard can be a bit more difficult, but if you modulate the cutoff frequency by the keyboard position, there should be a setting that will map the tuned noise to a proper scale. Alternately, you can just sample the tuned noise and map it to your keyboard that way.

• White noise by itself is pretty damn versatile, but sooner or later you may find yourself wanting something more complex and organic. Get out your favorite sampling mic and venture out into the world around you. Noise is everywhere. Try sampling yourself exhaling heavily, or blowing across a length of PVC pipe. Sample some noise off of an old cassette, answering machine (remember those?), or VHS tape. Crumple up or rip some paper. Pour some water. Whip a small stick very rapidly over your mic. Even just sample the ambient noise of the room you're in. Take a nice long section of one of these recordings, loop it, and layer it just slightly behind your standard synth pad/string sound and suddenly your pad becomes a lot more interesting. Be sure to program the amplitude envelope of the noise to match that of the pad for best results.

• Noise can add impact, too. A short burst of noise (controlled with a short amplitude envelope) can sound great at the beginning of a percussive bass sound. Add a little slightly behind an aggressive lead too to add interest.

Do you have any favorite techniques for using noise in your sound design? Let us know!


Anonymous said...

Great info. I've never given much thought to the noise generator. Now I have a new knob to play with.

"White" noise contains all audible frequencies at random. Just like white light contains all the colors of light. "Pink" noise displays the same pattern visually/mathematically as the color pink does in light. This is my basic understanding anyway.

In regards to origin, the math behind white noise was is a modification of the math used in Brownian motion. Brownian motion mathematics have been used for everything from particle physics to stock market projections. Yet another theory that failed to incorporate human greed. Get it? in-corporate...ah never mind.

The short version: Brownian Motion is an equation for random number generation.

Le Wiki:


Tom said...

Thanks, W!

Mad Al said...

It's related to the spectrum of light frequencies compared to the spectrum of audible sound frequencies. Red light is at the low frequency end of the light spectrum, so white noise that has been filtered to attenuate the high frequencies (making it more low frequency heavy) is called pink (the same way in astronomy light that has effectively slowed due to the source and receiver moving apart is "red shifted").

As far as the actual audio process, it has to do with making the amount of power the same across octaves. Each successively higher octave has twice the frequency range of the octave below, and if all frequencies are present at equal amplitude, each higher octave will have twice the power of the previous octave. This will lead to the higher octaves sounding louder... which is why white noise sounds to us like it has more high frequency content.

As for Brownian motion... I still like Douglas Adam's favourite source, a nice hot cup of tea.

Anonymous said...

I knew 10 minutes of Google tea would produce a concise response.

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Javi said...

I like to use Noise as a modulation source of the filter freq in some synths like the NI Pro53 plug in. It ads overdrive, works well with a bit of resonance.