Electronics theory for guitarists

sev112 · July 31

So I love music theory, it al seems so simple

but what I have never understood is how electronics, and in particular sounds into electronics back into sound again (whether analogue or digital) works from a guitarist’s point of view.

any good resources / links that help to understand that

few kinds of questions I am flummoxed by

why does a single tone have a sinusoidal wave form, why does it cycle above and below the axis and why is it smooth?

I can understand that when you put harmonics on top of that, and then other notes such as in a chord or from other instruments at the same time, how on Earth can a microphone discern all of those signals and then make them sound exactly the same when we plug them into an amp and speaker?

my guitar has 6 strings, 22 frets, harmonica, differentbpicking techniques, whereas a speaker has a single cone - how does it replicate all a guitars sounds?

etc

please no £50 book recommendations; web links would be useful

ta v m

PS still got Covid, and fed up with the Olympics !

Danny1969 · July 31

Well a microphone or guitar or speaker are devices that produce or recreate AC currents. That's the most important thing to consider. An AC current has a zero position and it swings either side of that. Like a child on a swing, if the swing is at rest then that's 0V and it swings either side to positive and negative voltages in respect to that 0V position. Faster it swings the higher the frequency.

So a sine wave starts at zero volts then climbs to a positive voltage then back to 0 then below 0V to a negative voltage. (could be the other way round depending on the phase polarity of the input signal) The faster it does these cycles the higher the note you hear . Only signal generators and synths tend to produce smooth sine waves, almost everything else has far more complex waveforms .

You can consider a moving coil microphone like an SM58 and a speaker to be the same thing. The both operate in exactly the same way. You can use a speaker as a microphone or a microphone as a speaker ... I mean you wouldn't want to but both have an at rest position and both can swing either side of that to positive and negative voltages in respect to that at rest position. A guitar pickup can be considered the same but with no moving parts it's hard to use it as a microphone or a speaker but there is a tiny bit of that action happening in the vibration of the coils ... likewise an output transformer in a valve amp.

What's hard to understand is all these waves of AC are being made at the same time and somehow the pickup can capture that and the speaker can reproduce it. This seems impossible but in reality even the most complex waveforms can be broken down into combined simple sine waves so if a speaker is producing a steady 50hz tone and you introduce an 800hz tone at the same time then the speaker will keep doing the 50hz but now with an additional movement at 800 as well in the form of judder superimposed onto the 50hz and so on

So that's how a speaker does it and a microphone or a guitar pickup is a speaker used in the inverse direction

randella · August 1

Danny1969 said:

Well a microphone or guitar or speaker are devices that produce or recreate AC currents. That's the most important thing to consider. An AC current has a zero position and it swings either side of that. Like a child on a swing, if the swing is at rest then that's 0V and it swings either side to positive and negative voltages in respect to that 0V position. Faster it swings the higher the frequency.

Understanding that you can superimpose an AC swing on a steady DC potential gets you quite a ways towards figuring out how valves and transistors are used to amplify a signal.

If you're after understanding more of that, google Rob Robinette for starters. Uncle Doug's YouTube channel has some good lessons in the basics of amplification too.

I think the questions there are more tending towards the physics of the waveform which is a whole other rabbit hole, I'll leave that to others!

Sporky · August 1

Sine waves are the basic building block of pitched sound; all other pitched sounds can be created from them. It gets more complex when the sound changes over time, but let's leave that for now. They're smooth because they have no harmonics. Square waves have sharper edges because of higher frequency content.

Microphones don't capture all the individual sine waves. They capture the overall soundwave. They done care how it was made, they just respond to the pressure waves in the air and create a signal that represents that wave. Loudspeakers do the opposite; the signal drives the cone, which creates pressure waves in the air. We perceive those as sound.

The Science Of Sound (Thomas Rossing) is still my favourite book on the subject - you can find used copies for £20 or so.

viz · August 1

The combination of various sine waves into complex waves with all their harmonics and timbre is described by Fourier and the Fourier transformations. And it can be done backwards too - any weird wave shape can be deconstructed into individual sine waves. Check it out

randella · August 1

@Sporky - had a quick look, but they seem closer to £40. My Uni library has a couple of copies though, so going to give that a bash. Ta for the recommendation.

Sporky · August 1

They do pop up for £20ish from time to time, honest.

randella · August 1

Yep, no doubt - in fairness I did the most cursory search possible before remembering where I might be able to borrow a copy for the princely sum of nowt

Sporky · August 1

Which is even better value!

sev112 · August 1

Very well described ! Ta

So, if it requires to be AC, can we use DC ?

randella · August 1

Audio signals are representing fluctuations in air pressure - 'heard' by a microphone, or voiced by a speaker. The more rapid the fluctuation, the higher the frequency of the sound.

DC is steady state - think like a battery. One terminal is at a potential, i.e. 1.5V for a double-A. The other terminal is held at 0V. The 'potential difference' is the voltage that the battery can deliver when current flows from one terminal to the other.

I wouldn't recommend you try this, but you can put a 9V battery onto the terminals of a speaker. What you'll see, depending on which way around you make the connection, is the speaker cone move either in or out and stay there. The coil has been energised with a current flowing in one direction only.

You want the coil to be energised one way and then the other, to pull the cone in and push it out according to the frequency represented by the AC signal.

Sporky · August 1

sev112 said:

Very well described ! Ta

So, if it requires to be AC, can we use DC ?

I don't think the AC and DC stuff is very helpful to the questions you originally asked.

Signals and mains power are AC. Most (but not all) low voltage power supplies are DC.

But calling signals AC is, to my mind, confusing.

Danny1969 · August 1

Audio signals are alternating current . All the manipulation we do such filters, tone controls etc using capacitors and inductors wouldn't even be possible with DC as it's the exploitation of reactance that makes this possible. And blocking DC from stage to stage while letting the audio component pass through etc

This is why I described a 9V power pedal circuit as the power supply cut in half ... in order to allow the audio signal to swing both ways. Generally because Audio is AC we need a dual supply ... particularly for opamps but by choosing the halfway point of the battery we cam mimic the centre tap of a transformer and make (a rather shit) dual power supply that can swing both ways like the audio signal

randella · August 1

Sporky said:

sev112 said:

Very well described ! Ta

So, if it requires to be AC, can we use DC ?

I don't think the AC and DC stuff is very helpful to the questions you originally asked.

Signals and mains power are AC. Most (but not all) low voltage power supplies are DC.

But calling signals AC is, to my mind, confusing.

Aye you're probably right. I was thinking as I was typing that it gets tricky to explain things that you learned and internalised a long time ago!

Sporky · August 1

Danny1969 said:

Audio signals are alternating current

Yes - I'm not saying what you posted was incorrect, but I don't think that helps answer the original questions, and getting into this sort of detail early on risks confusing people.

Better, to my mind, to start by answering the original questions simply and clearly. Then we can expand from there.

Danny1969 · August 1

Well the original first question was

"but what I have never understood is how electronics, and in particular sounds into electronics back into sound again (whether analogue or digital) works from a guitarist’s point of view"

If you understand that from guitar to speaker you are just starting with a tiny AC signal and then making it much larger via voltage and current gain (power) then it's easy to understand.

What confuses some people is they seem to think the guitar pickup signal is DC ... they even use the term 8K resistance or similar to describe a pickup which is nonsense when describing a giant inductor

Musicwolf · August 1

I'll throw Measured Tones by Ian Johnston in as a recommendation.

Image: https://qph.cf2.quoracdn.net/main-qimg-78e4c977f139f8fe121249cea08201c1-lq

I think that the paperback version is about £30.

Once you get your head around the physics then the electronics side is quite straight forward.

jpfamps · August 1

sev112 said:

how on Earth can a microphone discern all of those signals and then make them sound exactly the same when we plug them into an amp and speaker?

The mic, amp and speaker signal chain doesn't discern all those signals.

These elements see a changing voltage, that's all.

The fact that the ear / brain can interpret this as music doen't mean that it's more complicated for the system to amplify than any other wave form.

That's anthropomorphism thinking.

UnclePsychosis · August 19

To answer one of your questions - its not that a single tone happens to be sinusoidal, it's the other way around. If you create a perfectly sinusoidal acoustic wave, then your brain interprets that as a single tone. The definition works the other way round to your question!

sev112 · August 19

Yeah, I saw clip sometime of the frequency of a “hit” of something increasing from 1 Hz and increasing and it’s the repeated hits that combine and make the tones we hear as single

Axe_meister · September 4

Check out the Wampler Youtube channel for more FX based electronics he explains things very well.

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Electronics theory for guitarists

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