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8 March 2015

The colour of noise

I'm not sure really what today's post is going to be about. I'm going to do some free-writing and let's just see where we end up...

Events have put a break on my project-work. Just as well really, because look at the state of my cave! I've been forced into some long-overdue tidying up.

"Tidy desk, tidy mind"

I'm a proponent of this school of thought. It took a while, but I managed to eat two big tubs of chocolate this morning just so I can store my wire and resistors neatly. Do you sense that I have time on my hands?  

Something else that I never seem to find the time to do is to label my plugs. It can save loads of time and frustration if you do.

 This here is a picture of my effects pedal power supply. The bloody thing crapped out yesterday. It produces no voltage any more and is causing a strange sort of echoing click sound when plugged into my Piezo Buffer circuit. Damn, damn, damn!

I'd like to say that it was something I did that caused it to melt down, but I haven't got a clue what happened. Damn, damn, damn!

I blogged about my Piezo Buffer project yesterday and quickly got back to trying to fix that noise issue I mentioned. One thing that I've seen stated in my research is that you can never truly know how a circuit will perform until it is fitted in its enclosure. In fact, one place I saw it written had those words of wisdom in bold, italicised and underlined. Pah!

I'm not one for dramatics, but yeah, it's certainly something to rule out in my quest to end background "hum". I haven't decided how I'm going to box my circuit yet, but given that it is an audio device I'm building it would certainly make sense for the enclosure to be metal.

It was the natural philosopher Michael Faraday who once said: "I have far more confidence in the one man who works mentally and bodily at a matter than in the six who merely talk about it."

Wise words from the gentleman who brought us the Faraday Cage in 1836. Put simply the Faraday Cage is an enclosure made of conductive material that blocks electric fields. It's the guiding principle for protecting electronic circuits and is why electric equipment is usually housed in metal cases. And now you see where I'm going with this ramble... yes... I set out to test my circuit in a metal box to see if it made any difference to the annoying noise I've been hearing.

Sadly, my power supply crapped out before I managed to check this out fully and my heart wasn't really into using a battery. I'll have to wait until my replacement supply arrives. Wouldn't it be really annoying if that blew up for the same reasons that the first did! Ha ha.... doesn't bear thinking about.

Check out this retro bit of electronics. What are these "cassettes" you talk of?

In my travels across the internet this week I happened across a fantastic article on "Op Amp Noise Theory and Applications". Actually, it's not really an article, but an extract from a book called "Op Amps for Everyone" produced by Texas Instruments. The author is obviously trying to make the subject sound exciting and fun, but there's only so much you can do to spice up Op Amp Theory. Being the sad sort of person I am... I read it.

One of the things I learnt is that there are 5 types of noise experienced in circuits:

1) Shot Noise
2) Thermal Noise
3) Flicker Noise
4) Burst Noise
5) Avalanche Noise

I love this quote on Flicker Noise: "Flicker noise is also called 1/f noise. Its origin is one of the oldest unsolved problems in physics. It is pervasive in nature and in many human endeavors. It is present in all active and many passive devices. It may be related to imperfections in crystalline structure of semiconductors, as better processing can reduce it."

One of the things I've learnt about electronics these past couple of months is how imprecise everything is. I had in my head that everything was known and exact. Not so. As we saw above, flicker noise is "one of the oldest unsolved problems in physics". The manufacture of electronics components is so hit or miss that they come with quoted "margin for error". One of the fundamental techniques for figuring out the maths of physics is "simplification" where "close" is good enough. Who'd have thought?

I've always wanted a device with a "Brill" switch. Wouldn't it be great to switch Brill to maximum! Ha ha.

Back to noise...

Everyone's heard of "white noise", right?  Wikipedia describes white noise as "a random signal with a constant power spectral density". I've never given the term much thought. Imagine my surprise then to discover that another way of describing noise is by colour.

Being colour-blind I'm now wondering whether I hear noise different to other people? ;-D

I take no credit for the detail in the picture above. These are the different colours of noise as presented in "Op Amps for Everyone". See that "White" is right in the middle and the different colours are really just a way of categorising noise by where they sit in the audio spectrum. It's all based upon frequency.

"That's all very interesting," I hear you say, "but how does this help us to figure out how to stop that strange humming noise in your Piezo Buffer circuit?"

The sad truth is that I don't think that it helps at all. Damn. But it's quite interesting.... no?

I leave you with a picture of a dead crow in a tree.

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