Analog Noise Generator, Fighter Of Other Noises

A chaotic drone of meaningless sound to lull the human brain out of its usual drive to latch on to patterns can at times be a welcome thing. A nonsense background din — like an old television tuned to a dead channel — can help drown out distractions and other invading sounds when earplugs aren’t enough. As [mitxela] explains, this can be done with an MP3 file of white noise, and that is a solution that works perfectly well for most practical purposes. However he found himself wanting a more refined hardware noise generator with analog controls to fine tune the output, and so the Rumbler was born.

It’s a tight fit, but it does fit.

The Rumbler isn’t just a white noise generator. White noise has a flat spectrum, but the noise from the Rumbler is closer to Red or Brownian Noise. The different colors of noise have specific definitions, but the Rumbler’s output is really just white noise that has been put through some low pass filters to create an output closer to a nice background rumble that sounds pleasant, whereas white noise is more like flat static.

Why bother with doing this? Mainly because building things is fun, but there is also the idea that this is better at blocking out nuisance sounds from neighboring human activities. By the time distant music (or television, or talking, or shouting) has trickled through walls and into one’s eardrums, the higher frequencies have been much more strongly attenuated than the lower frequencies. This is why one can easily hear the bass from a nearby party’s music, but the lyrics don’t survive the trip through walls and windows nearly as well. The noise from the Rumbler is simply a better fit to those more durable lower frequencies.

[Mitxela]’s writeup has quite a few useful tips on analog design and prototyping, so give it a read even if you’re not planning to make your own analog noise box. Want to hear the Rumbler for yourself? There’s an embedded audio sample near the bottom of the page, so go check it out.

For a truly modern application of white noise, check out the cone of silence for snooping smart speakers.

10 thoughts on “Analog Noise Generator, Fighter Of Other Noises

    1. As far as I know part of why that’s done is to specifically make noise in the tones of human speech to lower the range of intelligible hearing in an environment like an office.

    2. I would ditch the Zener noise source and the 20V supply, a noisy OpAmp with a high impedance at its input can do the same. Bonus: using a low-voltage OpAmp like the LMV324 allows this thing to be powered by one quiet Li-ion cell = Noise without additional noise. Maybe add a TDA8551 or similar and ditch an external amplifier too.

  1. Back in my college days, I had a Commodore 64 in my dorm room hooked up to a small amp and a big speaker. I made a little program to enable the noise generator and set up a low-pass filter on it before playing to the speaker. This was my way to block out the noise from the other dorm folks in order to get a decent night’s sleep.

    The various things I’ve set up since then have all had various shortcomings. Some noise programs available on Android have glitches when looping. Sometimes they cut off in the middle of the night for no reason. Lots have too much high frequency content. (I use my phone with a BT speaker for this when traveling. At home, I’ve got a fan-based machine.)

  2. “there is no “undo” button
    there is no version control
    there is no ability to save your progress, except for taking a photograph, or tediously tracing out the schematic, which is prone to mistakes
    if something breaks, it’s never clear if that’s because of a change you made, or just a loose connection on the breadboard
    making mistakes means parts break, either spectacularly exploding, or worse, silently failing.”

    Do not know what planet the author is from, but on this rock none of that is true for any place I have worked at in the past 35 years.

    1. Furthermore:
      1) “there is no ability to save your progress.” Um, how about, don’t yank everything out of the breadboard? The only reason we have to save things on a computer is because they tend to go away when the computer is shut off. This usually isn’t the case with breadboards.
      2) Author says that turning a TV to an empty channel doesn’t work in the age of digital TV. Okay, how about an old FM radio (one that doesn’t mute between channels), then?

      1. While I think the paragraph is rather odd, I actually get the lack-of-saving point. Sometimes when I’m working on a breadboard I’ll end up going down a dead end fiddling with things, and wish I had some sort of magical wand so that I could roll back to the last working version

  3. [mitxela] says: “As this ambient audio softly sends me to sleep, I can be safe in the knowledge that the rednoise rumble is cryptographically random.”

    With that 20V switching boost converter in there it isn’t.

    1. >With that 20V switching boost converter in there it isn’t.

      You can reduce the influence of the switch mode supply by making its switching frequency outside of your circuit’s frequency response. Switch mode supply are every where, so you might want to learn living with them.

      e.g. For something like an *audio circuits*, operates the switcher at 200kHz or higher.

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