Tag: Retro Synth

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So Much Noise

Did you know that there is a technical definition of noise? Did you know that there are six main colors of noise? The most common type of noise is white noise, which consists of random fluctuations such that there is equal energy content per bandwidth. This can be thought of as being similar to a flat frequency response. Pink noise consists of random fluctuations with equal energy per octave. Brown (also called Red) noise consists for random fluctuations where the energy level of each bandwidth is related to the squared inverse of the frequency (1/f2). When listening to these three types of noise, it sounds like pink and brown noise are progressively lower in frequency than white noise. That is because more of their energy is concentrated in lower frequencies in comparison to white noise.

Blue noise features energy levels that are proportional to frequency, resulting in a 3dB increase per octave. Violet (or Purple) noise utilizes energy levels that are proportional to the square of the frequency, resulting in a 6dB increase per octave. When comparing blue and violet noise to white noise, they will sound higher in frequency than white noise, as increasing amounts of their energy is concentrated in higher frequencies. Finally, Grey noise is basically white noise that has been filtered to correspond with equal loudness curves, so that the while the energy level of each bandwidth will not be measurably equal, but will be perceived by human beings as being the same loudness.

To demonstrate white noise, I generated four seconds in Logic Pro’s Retro Synth. You can listen to the results below. On the first pass, the waveform is displayed in Audacity, on the second pass it is displayed as a spectrum in Logic Pro.

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Subtractive Synthesis Waveforms in Logic Pro’s RetroSynth

If you’re like me, you may wonder, how accurate are the waveforms in LogicPro’s RetroSynth subtractive synthesis emulator. It turns out, they’re pretty accurate. I tested the sine, triangle, sawtooth, square and pulse waves. At first glance, RetroSynth seems to only offer triangle, sawtooth, square, and pulse waves (noise as well, but that’s for another day) . . .

However, if you look at the amplifier portion of the emulator, there is a knob labeled “Sine Level.” Thus to get a sine wave, you have to pull down the filter CF all the way to the bottom, and pull up the Sine Level . . .

For the test I put in a whole note with a key velocity of 100 for each waveform. I used the note A1 (middle C=C4), resulting in a 55 Hz tone. You can see and hear the results in this video . . .

Note however that there are some weird artifacts during the square wave, which come from data compression.

Those of you who know your waveforms know that a sine tone is a pure tone that has no overtones (harmonics). A triangle wave is a sum of all the odd harmonics, where the fundamental is harmonic 1, with the amplitude of each partial is 1/(n squared). A sawtooth wave features all harmonics with an amplitude of 1/n. A square wave includes all the odd numbered harmonics with the amplitude of 1/n. A pulse wave is a variable square wave, and the harmonic content is reliant upon the width of the pulse. I used a graphic equalizer in Logic Pro to display the harmonic content of each waveform.