Starship noise generator

[Tantal]

For one of my projects (pimped scale model of Battlestar Galactica) I'm looking for a sound generator, that simulates the noise of a starship engine. Something like this here:


My first idea was to use brown noise with a low pass filter. But that might sound to synthetic. A little bit of humming and wobbling would be nice ;-)

I have never worked with oscillators or sound ICs before, so I'd appreciate any source of information.

[PeterFW]

I have never worked with oscillators or sound ICs before, so I'd appreciate any source of information.

Ask google for "noise box", "wired sound generator", "drone synth", "drone box" or "dronebox", that should get your started.
Then couple that with a voltage controlled bandpass and a few occilators.

Have a look at this one:

[tobia]

I downloaded a piece of that spaceship sound (using the excellent youtube-dl) and run a spectrum analysis on it with Audacity.

The result in in the first picture. It has a big lump of sound at 53Hz (-12.1dB in my picture) which is a very low rumble, very loud and yet barely audible, the stuff of subwoofers; then another component at 189Hz (-20.4dB) which is a distinct low rumble, above subwoofer range, with more detail for the "engines" sound; and finally many higher frequency sounds, up to 10kHz, which make up the "flares" part of this complex sound effect.

A brown noise has a very different spectrum. In the second picture you can see a standard brown noise, as generated by Audacity, superimposed on the spaceship graph. You can see how it's a very different sound, in fact it sounds nothing like it. You could approximate the general shape of the spaceship sound by low-pass filtering your brown noise, probably with a 53Hz cutoff frequency and the right rolloff rate, but it would still sound very different.

For a project like yours, I would worry more about the practical details of producing such a low sound, than about the sound itself. Traditionally one would need a very large speaker and high driving power to make low sounds and that's going to be a problem for a small model. As for the sound itself, I wouldn't try to synthesise it. I would just take a few seconds of it, put it on an eeprom and get a run of the mill PCM decoder chip to play it back.

Actually that's how you would do things 10 or 20 years ago. Nowadays you can solve both problems with one of those $5 mini portable speaker mp3 players (eBay is full of them, they look like picture 3.) If you need to control it, you can wire its buttons to your MCU trough some optocouplers (I have done it with good results for a project of mine.) Otherwise just leave it as it is and turn it on manually through a hatch in your Battlestar model. You may want to glue the player to the bottom or to the largest piece of your model, to use the structure itself as a resonator for the speaker. I may be wrong, but I think that's why those things sound much better if you put them on a table than if you hold them in the air.

[Tantal]

Thanks a lot for your efforts!

Actually that's how you would do things 10 or 20 years ago. Nowadays you can solve both problems with one of those $5 mini portable speaker mp3 players ...

I still want to do it the old-fashioned way. Out of curiosity. And because, right now, I know nothing about how to design filters, frequency synthesis, etc. - and I want to learn.

Questions: Can I use FFT to compose this sound out of 3-4 single frequencies (53Hz, 189Hz, ...)? And if so, how would I generate one specific frequency, lets say 53Hz, with circuitry (not using microcontrollers)? And how would I create a low pass filter with a specific cutoff frequency (again without using microcontrollers)?

That's the stuff I would like to learn.

P.S.
I removed "Arduino" from the subject line.

[T3sl4co1l]

Guessing by ear, I'd say low-passed noise?

Judging by the spectra (thanks!), I'm right.  The open question being, how much lowpass to perform; true brown noise is the integral of white noise, which has a low-pass characteristic, but undefined DC and high amplitudes of nearby (low rumbling).  The ear doesn't resolve such low frequencies anyway, so perhaps one might simply say we won't integrate below 50Hz or so.  Which is to say, simply a low-pass with a cutoff of 50Hz.

Evidently, a -40dB/dec slope (a 2nd order lowpass) is the way to go.

Add in some low frequency components and/or harmonics (which could be from an oscillator, give or take waveshaping to get a certain harmonic profile), or maybe just tighter filtered noise (which would have more of a "sounds like the far end of a long pipe" kind of sensation), which can be done with a high order filter or PLL, and you should have about the right idea.

Tim

[G7PSK]

Star ships make no sound or at least you cant hear them as sound dose not travel in a vacuum, why no one hears you scream when run over by a star ship .

[Seekonk]

Did a plane display and used a UNO to animate it lights, motion, and sound.  Did a couple random number generators into tone and some other stuff.  It sounded like a jet engine with occasional pac man. Ended up just what I wanted. It never got better than the first try.

[MatthewEveritt]

Star ships make no sound or at least you cant hear them as sound dose not travel in a vacuum, why no one hears you scream when run over by a star ship .

Definite geek-cred for making the noise generator then putting it in an evacuated chamber so you can't hear it.

[Tantal]

Add in some low frequency components and/or harmonics (which could be from an oscillator, give or take waveshaping to get a certain harmonic profile), or maybe just tighter filtered noise (which would have more of a "sounds like the far end of a long pipe" kind of sensation), which can be done with a high order filter or PLL, and you should have about the right idea.

Besides some very basic circuits (voltage divider, full-wave rectifier with 4 diodes) and a little bit of Arduino programming I am completely new to electronics. Can you please give me a couple of phrases that I could use on Google to point me into the right direction?

[PeterFW]

Star ships make no sound or at least you cant hear them as sound dose not travel in a vacuum, why no one hears you scream when run over by a star ship .

That is not entirely correct, it depends on the drive used.
A big gravity drive will resonate at a frequency below 5Hz but has harmonics in the range com 500Hz to 8Thz.
When you are near enough to be in the spatial compression wake the bones in your inner ear will experience a gravity differential in respect to each other and the sourrounding bone,

You will be able to hear those "vibrations", even in a vaccuum. Granted, the range of that effect is fairly limited but it is notiveable close range.

[tobia]

Tantal, I'm a newbie too! I'm still going through Practical Electronics for Inventors, because I want to have the basics down first, but I'll certainly delve into audio syntesis next.

In fact, prompted by your query I found a nice book called Make: Analog Syntesizers (free sample chapters here). It looks like it goes from zero (breadboard, multimeter, soldering technique, rectifier circuit…) up to building cool analog synths like this one:



This one makes some really cool sounds and it's not at all complicated (schematics here). I can count two chips (just opamps, which are rightful citizens of the analog landscape), three transistors, and a bunch of resistors and capacitors.

I just found out about the book, but it might just be what you're looking for. The publisher and the Make brand certainly have a great reputation.

[tobia]

When you are near enough to be in the spatial compression wake the bones in your inner ear will experience a gravity differential in respect to each other and the sourrounding bone, you will be able to hear those "vibrations", even in a vacuum.

That's really cool!

But certainly the classical "starship noise" from movies and tv shows was meant to represent the noise you'd head on board the ship, where the vibrations of engines and other machinery would propagate to habitable zones through the structure itself.

[dentaku]

You got me interested in making a spaceship background rumble sound because I've never done that before.
I used 3 noise generators from Ableton Live's Operator softsynth, a resonator, chorus, distortion and a convolution reverb. I have no cue how you'd do that with basic hardware.

The effects are the problem. Creating some noise sources then lowpass filtering them with different cutoff frequencies isn't terribly complicated but it won't sound like your example or my attached .MP3.

I've created white noise with the simple circuit at the top of this page before. http://www.experimentalistsanonymous.com/ve3wwg/doku.php?id=noise_generator
It uses an NPN transistor that has the collector connected to nothing

[T3sl4co1l]

Besides some very basic circuits (voltage divider, full-wave rectifier with 4 diodes) and a little bit of Arduino programming I am completely new to electronics. Can you please give me a couple of phrases that I could use on Google to point me into the right direction?

Sure--

https://www.google.com/search?&q=white+noise+circuit&oq=white+noise+circuit (the one on EDN is pretty standard, and will work -- arguably, too simple for even EDN to screw it up! )

https://www.google.com/search?q=2nd+order+low+pass+filter+calculator (the Okawa-Denshi calculators are reasonable; mind: if you put in UNreasonable component values, you will get unreasonable values out!  It's a calculator, not a designer.  Sanity is your responsibility. )

A Sallen-Key or MFB topology, with Butterworth characteristic, is an absolutely standard way to go, and gives good results.  (You can use the other half of that LF412, instead of using the x100 output in the EDN circuit.)

Tight filtering can be harder.  The general approach is to make a nearly unstable amplifier, by putting resistors and capacitors into the feedback loop.  Or to put it another way, making a modest quality LC resonator, by faking the inductor with an op-amp and capacitor (op-amps can be used to convert and invert impedances!).  You'll see this for bandpass or "frequency boost" types of circuits.

(Oops, dropping more terminology; give "LC resonant tank circuit" a look.  Basically, the electronic equivalent of a mass and spring.)

Another approach is to set up an oscillator, and control its frequency based on some comparison with the input signal (which in this case, would be the white noise).  When the comparison is done with a phase detector or RF mixer, the result is called a PLL (phase locked loop).

A PLL can be expressed as a kind of bandpass amplifier, though usually with much better performance than you'd get from trying to make a brute-force filter.  They're also much quirkier (lock/unlock behavior, nonlinearity), and can be more useful (the frequency control voltage has useful properties, like tracking frequency modulation -- intuitively, a PLL following an FM signal must have the original signal controlling its own oscillator, right?).

https://www.google.com/search?q=tone+detector
The old LM567 (and relations) is a classic.  It's an analog circuit, so is well suited to this sort of thing.  There should be example circuits that show this sort of function (narrow bandpass filtering).

(There are other kinds of "locked loops" besides PLLs.  Other detectors can be used, to get FLLs (frequency), DLLs (delay) and so on.  The "locking" generally refers to controlling one parameter (e.g., frequency, or say, mechanical servo velocity) based on a physical relation to the detected signal (phase, position), thus locking the parameter *exactly* in place, with no error).

Once you have your filtered signals, you can "OR" them together using an audio mixer.  The most basic version of this is, you take the output voltages from each block, wire them together with series resistors, and amplify.  Often, the amplifier is an inverting type, so all the resistors meet at a "virtual ground" (the op-amp holds -in = +in thanks to feedback), which prevents the signals from seeing cross-talk (more important in something like an audio mixing board than here, but an important lesson).

Tim