"The Electronics of Audio"

[mbenonis]

I'm in the process of writing a long article/short book on the electronics behind audio systems, and I'm looking for some input. What I'm about to post is a very rough draft - i.e., it hasn't been proofread, figures are not included, and many things are incomplete. What I would like to know is whether what I'm writing would be useful for anyone here, and if not, what could be added or changed to make it more useful.

Link: http://www.benonis.net/electronicsofaudio.pdf

 

[DaveySimps]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

Overall, a great document. Who is your target audience for the document? If you are looking at it as a intro document in some sort of traning program, it might be a bit too wordy / mathy (to coin a term). I am not really sure how to avaoid this, as it is an important part of understand electricity. If it is intended as more of an intro document, you might want to rely more on your anaolgies than the math / computation. I know when I was younger and first trying to understand this stuff, the concepts are what stuck in my head and helped me to learn, not the equations (although I am not undermining their importance) they can always be looked / referenced when needed.

As it was presented, it seemed to me that it is a document to explain the electronics of sound to engineering students. Although unavoidable to an extent, the article assumes some advanced math knowlege of the reader (cosine, logarithm, Kirchoff's Law), which could be a HUGE obstacale to many audiences. Just my $.02

~Dave

 

[mbenonis]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

Overall, a great document. Who is your target audience for the document? If you are looking at it as a intro document in some sort of traning program, it might be a bit too wordy / mathy (to coin a term). I am not really sure how to avaoid this, as it is an important part of understand electricity. If it is intended as more of an intro document, you might want to rely more on your anaolgies than the math / computation. I know when I was younger and first trying to understand this stuff, the concepts are what stuck in my head and helped me to learn, not the equations (although I am not undermining their importance) they can always be looked / referenced when needed.

As it was presented, it seemed to me that it is a document to explain the electronics of sound to engineering students. Although unavoidable to an extent, the article assumes some advanced math knowlege of the reader (cosine, logarithm, Kirchoff's Law), which could be a HUGE obstacale to many audiences. Just my $.02

~Dave

To be honest, I'm not sure exactly who I'm targeting at the moment. It is also quite possible that this will fork into two separate documents, one as an introductory piece that limits the math, and one that expands on that with math and circuits, etc.

The idea behind this is that I haven't found any good books that go into the electrical side of sound very much. There are plenty of technical books (like the Yamaha text and others) which talk about it in passing, and plenty of circuits books which talk about circuits more abstractly, but nothing that applies the circuits to audio. The other idea is to really emphasize some of the important concepts I've either discovered on my own or that books typically gloss over, such as a thorough explanation of decibels, etc.

I don't want this to be a text on electrical engineering, but rather what you need to know about how your equipment works so you can use it better and understand how to fix it when it's not working.

It may be that this is a "second level" text, after you've read the Yamaha text or some equivalent. I also don't mind writing a primer on the math (especially logs) as an appendix.

Everyone's thoughts are welcome here. These details should be fleshed out before I write any more, so I don't have to rewrite more.

 

[DaveySimps]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

I do agree that there are VERY limited resources out there for teaching the subject. I have looked and looked for info when teaching my Advanced Stagecraft class, and Sound Design Seminar, and there is really nothing. I have had discussions with Engineering faculty, and they agree with the gap in good info. Your "two seperate documents" idea might be a good way to resolve the idea. For me, I like that better than having to apply a primer. Keep up the good work. It is not an easy thing to do. Kudos to you for attempting it. From an academic standpoint, I would consider including somehting like this in a course packet for one of my classes, even if it was not an entire book.

~Dave

 

[philhaney]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

To be honest, I'm not sure exactly who I'm targeting at the moment. It is also quite possible that this will fork into two separate documents, one as an introductory piece that limits the math, and one that expands on that with math and circuits, etc.

The idea behind this is that I haven't found any good books that go into the electrical side of sound very much. There are plenty of technical books (like the Yamaha text and others) which talk about it in passing, and plenty of circuits books which talk about circuits more abstractly, but nothing that applies the circuits to audio. The other idea is to really emphasize some of the important concepts I've either discovered on my own or that books typically gloss over, such as a thorough explanation of decibels, etc.

I don't want this to be a text on electrical engineering, but rather what you need to know about how your equipment works so you can use it better and understand how to fix it when it's not working.

It may be that this is a "second level" text, after you've read the Yamaha text or some equivalent. I also don't mind writing a primer on the math (especially logs) as an appendix.

Everyone's thoughts are welcome here. These details should be fleshed out before I write any more, so I don't have to rewrite more.

1. Select a target audience before you write any more. Otherwise your document will meander around aimlessly in search of an audience. "Aim at nothing and you will hit it."

2. For your water analogy, try putting a water wheel in the sink for something to dissipate all that power (or make the whole thing a dam with a pipe (conductor) from the lake (voltage) that feeds the generator (power dissipator or load) which a valve (resistance) for flow control).

3. Chapter one reads like its title What is Audio, really? for the first paragraph. The rest of chapter one reads like a very condensed "Intro to Electronics" book. The question "what is audio" is like a decibel; it all depends on what you are using for a reference, or where you are in the audio chain (actually, it's waves of air pressure striking my eardrums that my brain interprets as sound). You might try something along the lines of "By the way, in order to properly understand the electronics of audio we need to go over a couple of things." and then have a chapter on electronic principles (or make it appendix B, right after the one about the math).

Please be advised that most of us on the left coast (I'm talking California here) were raised on E = IR and P = IE instead of V = IZ and P = IV so some of your symbols may be confusing.

...a much more intuitive explanation is that impedance is the opposition to current flow in a circuit. To go back to our sink analogy, the thinner our pipe is, the more impedance it exhibits...

Umm, impedence implies an AC component. For DC (like your sink) the circuit has resistance.

Oops! I'm going into nit-picky mode and I didn't mean to.

It's a good first draft, and I'm sure you'll go far with it. Thanks for posting it and allowing us to help you improve it.

 

[avare]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

A great concept. You stated clearly it is a work in progress, so I'll keep my comments in that vein.

As Phil wrote, identify the audience.

There seems to be meandering between DC and AC equations.

The references to AC do not have an explanation of the different measures, ie. peak, RMS, average.

Andre

 

[mbenonis]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

2. For your water analogy, try putting a water wheel in the sink for something to dissipate all that power (or make the whole thing a dam with a pipe (conductor) from the lake (voltage) that feeds the generator (power dissipator) which a valve (resistance) for flow control).

Not a bad idea here.

3. Chapter one reads like its title What is Audio, really? for the first paragraph. The rest of chapter one reads like a very condensed "Intro to Electronics" book. The question "what is audio" is like a decibel; it all depends on what you are using for a reference, or where you are in the audio chain (actually, it's waves of air pressure striking my eardrums that my brain interprets as sound). You might try something along the lines of "By the way, in order to properly understand the electronics of audio we need to go over a couple of things." and then have a chapter on electronic principles (or make it appendix B, right after the one about the math).

You bring up a good point. I might also simply need to write more about what audio is in the first chapter, and make chapter 2 the introduction to electronics.

Please be advised that most of us on the left coast (I'm talking California here) were raised on E = IR and P = IE instead of V = IZ and P = IV so some of your symbols may be confusing.

I'll be sure to define the symbols as I go along, and be consistent with them. In case you were wondering, I prefer to use V for voltage because E means Electric Field to me.

...a much more intuitive explanation is that impedance is the opposition to current flow in a circuit. To go back to our sink analogy, the thinner our pipe is, the more impedance it exhibits...

Umm, impedence implies an AC component. For DC (like your sink) the circuit has resistance.

Oops! I'm going into nit-picky mode and I didn't mean to.

To an electrical engineer, it does indeed. However, one of my goals is to make people always think in terms of impedance, even if the phase angle is zero. Nothing is truly frequency-independent, buy I think people tend to forget this (or never learn it to begin with). Maybe I'm being a bit naïve here though...

 

[philhaney]

Re: The Electronics of Audio

Not a bad idea here.

Thanks.

I'll be sure to define the symbols as I go along, and be consistent with them. In case you were wondering, I prefer to use V for voltage because E means Electric Field to me.

I see your point. You may want to explain the "E means electric field" thing in the book, though.

...one of my goals is to make people always think in terms of impedance, even if the phase angle is zero. Nothing is truly frequency-independent, buy I think people tend to forget this (or never learn it to begin with). Maybe I'm being a bit naïve here though...

As for people knowing that "nothing is frequency independent," that depends on which physics class they took in college (the community college I went to had three versions of the same class: no math required, trig required, and calculus required). For those that didn't take the calculus version you might induce confusion, although I'm not sure how you explain that using the left-hand rule for generators.....

 

[mbenonis]

Re: The Electronics of Audio

As for people knowing that "nothing is frequency independent," that depends on which physics class they took in college (the community college I went to had three versions of the same class: no math required, trig required, and calculus required). For those that didn't take the calculus version you might induce confusion, although I'm not sure how you explain that using the left-hand rule for generators.....

LOL. Yeah, I'll have to see how math-y I want to get. I do kind of see this (at least the non-intro document) as having a healthy amount of math. I mean, I'm not going to do volume integrals or solve Maxwell's equations, but basic differentiation and integration, imaginary numbers, and maybe a bit of signals (Fourier analysis) would be good to have. The math needn't be rigorous, and some hand-waving might be necessary, but there should be just enough math to make the point and have it be "correct" and not oversimplified - mainly because nobody else does it (as we know, there are *plenty* of introductory texts out there that will explain basic circuits, basic equations, etc. This is to be more than that - a step up.) Opinions?

 

[DaveySimps]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

I think that is a very valid approach; a nice way to focus the writing.

~Dave

 

[museav]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

I'll be sure to define the symbols as I go along, and be consistent with them. In case you were wondering, I prefer to use V for voltage because E means Electric Field to me.

But just about everyone else uses E in their texts and classes, so it probably makes sense to stay with that.


Pat Brown actually covers much of this information in the first part of the SynAudCon Sound Reinforcement for Technicians class, that might be a good reference.


Some topics that I think are very relevant specifically to audio rather than to general electronics include:

Impedance, reactance and resistance and why you can't use your typical VOM to measure speaker impedance.

Balanced versus unbalanced and the fact that balanced has to do with impedance and not signal symmetry (differential signals are a separate topic).

The effect of impedance on splitting and parallelling. Why can you more easily split to multiple high impedance inputs?

Power transfer (impedance matched) versus voltage transfer (low to high impedance). Why was 600 Ohm impedance matching so common in the past but not used now?

What is a "constant voltage" system?

How do transformers work?

What is phantom power, why do you need it and how does it work?

What is amplifier "gain"? Or simply the general idea of how an amplifier works, not so much the specific circuitry as things like it really being a voltage rather than power amplifier, what the input attenuators do (and the fact that they do not adjust the gain or potential output), how current limiting affects the maximum output, what bridging is actually doing, etc.

Line losses and damping factor.


Those are just a few topics off the top of my head, but if your audience is more audio folks than EE and electronics folks, then focusing on common issues and questions to explain the theory behind them might make it easier to read than just presenting theory.

 

[elite1trek]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

I don't want this to be a text on electrical engineering, but rather what you need to know about how your equipment works so you can use it better and understand how to fix it when it's not working.

I think this should be your main focus. Some math definitely is required, but try to keep it practical.

Its great.

 

[jkowtko]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

Some more tidbits of feedback --

* Chapter 1: audio isn't just a "type" of electrical signal, it's specifically a signal that can produce sound.

* mention the differences between digital and analog electronic sound signals. You don't have to elaborate too much on digital sound at all except to mention that it's there and is used (digital coax), and that the electrical pattern is very different from analog.

* so the focus of this document is then on analog, right?

* Suggest adding subchapter/section headings. Chapter 1 moves around between a lot of topics. It would be easier to navigate the chapter and use this as a reference guide if there were subchapter/section headings.

* Audience, I agree with others who say this would be a good primer/reference for technically savvy people and/or engineers who know electronics basics and want to understand pro audio equipment, how it works, and how to troubleshoot and resolve problems quickly. So in line with some of the above topic suggestions, add topics that will help you understand how to get better, cleaner sound out of your PA equipment:
- ground loop hum, how to detect and deal with
- dirty neutral, how to detect and deal with
- summing amps (in the boards), and in general the difference in signal quality between high quality and low quality boards.
- noise floor, and how it propogates through the system
- gain structures, how there are many stages of gain in a system, and how not setting them all reasonably well can produce clipping and/or high noise floors
- compressors, what's really happening inside
- wireless RF, the different types of noise and how to deal with

I know I personally would love to have a primer like the above. I own the Yamaha handbook, have read through the first few chapters, but it's a pretty big document and not sure it covers all of the issues above. A targetted doc specifically to help sound engineers would be great.

Thanks. John

 

[museav]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

FWIW, this looks to be potentially addressing several different general areas; audio related electrical (power, grounding, etc.), audio related electronics, audio related signals and signal transmission, the electronic system (system gain and so on) and the interface to the environment (transducers). That's a lot of ground to cover.

You might want to look at this recent book, Amazon.com: Audio Engineering: Know It All, Volume 1 (Newnes Know It All) (Newnes Know It All): Douglas Self, Julian Nathan, Ben Duncan, CHAS MILLER, Ian Sinclair: Books, it definitely seems aimed squarely at the audio electronics aspect.

 

[mbenonis]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

But just about everyone else uses E in their texts and classes, so it probably makes sense to stay with that.

I've yet to figure out why people do this...it's definitely not the "EE", or even the Physics way of doing it. Oh well...

Pat Brown actually covers much of this information in the first part of the SynAudCon Sound Reinforcement for Technicians class, that might be a good reference.

I'll take a look at that.

Some topics that I think are very relevant specifically to audio rather than to general electronics include:

Impedance, reactance and resistance and why you can't use your typical VOM to measure speaker impedance.

Balanced versus unbalanced and the fact that balanced has to do with impedance and not signal symmetry (differential signals are a separate topic).

The effect of impedance on splitting and parallelling. Why can you more easily split to multiple high impedance inputs?

Power transfer (impedance matched) versus voltage transfer (low to high impedance). Why was 600 Ohm impedance matching so common in the past but not used now?

What is a "constant voltage" system?

How do transformers work?

What is phantom power, why do you need it and how does it work?

What is amplifier "gain"? Or simply the general idea of how an amplifier works, not so much the specific circuitry as things like it really being a voltage rather than power amplifier, what the input attenuators do (and the fact that they do not adjust the gain or potential output), how current limiting affects the maximum output, what bridging is actually doing, etc.

Line losses and damping factor.

These are all excellent topics that I'd like to cover. Some of these areas are things I don't completely understand too, but this will be a great learning experience for all involved (author and readers).

Those are just a few topics off the top of my head, but if your audience is more audio folks than EE and electronics folks, then focusing on common issues and questions to explain the theory behind them might make it easier to read than just presenting theory.

You do raise a good point here, and I do want this to be an audio-focused book. Perhaps a good format might be small chapters with specific subjects. This would also facilitate writing the thing, since it can be done in small chunks as I have time.

 

[mbenonis]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

Some more tidbits of feedback --

* Chapter 1: audio isn't just a "type" of electrical signal, it's specifically a signal that can produce sound.

* mention the differences between digital and analog electronic sound signals. You don't have to elaborate too much on digital sound at all except to mention that it's there and is used (digital coax), and that the electrical pattern is very different from analog.

Good points here. I don't want to get into Digital too much at this point, though I'd be open to it later on. Any Digital I would do would focus on the electrical side and not the format or anything like that.

* so the focus of this document is then on analog, right?

Yes, at least initially.

* Suggest adding subchapter/section headings. Chapter 1 moves around between a lot of topics. It would be easier to navigate the chapter and use this as a reference guide if there were subchapter/section headings.

My thought is to make the text less traditional, and focus on small chapters (see above). That would also make it easier to use as a reference.

* Audience, I agree with others who say this would be a good primer/reference for technically savvy people and/or engineers who know electronics basics and want to understand pro audio equipment, how it works, and how to troubleshoot and resolve problems quickly. So in line with some of the above topic suggestions, add topics that will help you understand how to get better, cleaner sound out of your PA equipment:
- ground loop hum, how to detect and deal with
- dirty neutral, how to detect and deal with
- summing amps (in the boards), and in general the difference in signal quality between high quality and low quality boards.
- noise floor, and how it propogates through the system
- gain structures, how there are many stages of gain in a system, and how not setting them all reasonably well can produce clipping and/or high noise floors
- compressors, what's really happening inside
- wireless RF, the different types of noise and how to deal with

Another great set of topics (especially RF - believe me, there will be quite a bit on that). As I said for the above set, I'm not completely comfortable with some of these topics, but I will do my best to learn them and and make them accessible to others.

I know I personally would love to have a primer like the above. I own the Yamaha handbook, have read through the first few chapters, but it's a pretty big document and not sure it covers all of the issues above. A targetted doc specifically to help sound engineers would be great.

Thanks. John

I too have the Yamaha text, and while it is a great book it suffers from being too broad to be useful in understanding the electronics side of things. Hopefully this will cover that better.

 

[mbenonis]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

FWIW, this looks to be potentially addressing several different general areas; audio related electrical (power, grounding, etc.), audio related electronics, audio related signals and signal transmission, the electronic system (system gain and so on) and the interface to the environment (transducers). That's a lot of ground to cover.

You might want to look at this recent book, Amazon.com: Audio Engineering: Know It All, Volume 1 (Newnes Know It All) (Newnes Know It All): Douglas Self, Julian Nathan, Ben Duncan, CHAS MILLER, Ian Sinclair: Books, it definitely seems aimed squarely at the audio electronics aspect.

I hadn't seen this. It looks like it won't be out for a bit, but I'd be really interested to see what it covers and how it covers it.

I will say this, though: I intend for my book to be open, in the sense that it will be free and open to revision as necessary.

Also, I would not necessarily object to having others write chapters for this (with full credit given as author of that section). It's a large project, and everyone has their specialties. Not only would this improve the quality of the product, but it would also potentially allow it to be written more quickly.

 

[museav]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

The comment about different people writing different chapters reminded me that there is also supposed to be a new edition of the Handbook for Sound Engineers coming out in October or November.

 

[church]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

The advice to identify your audience is absolutely correct. There are good texts out there, on the internet, in books, on manufacturers websites etc that provide great insight. Many are not written by engineers and provide excellent insight gained by years of working in the field. However as always you have to read many sources and to gain an in depth understanding that allows you to istill the key information for a target audience. You are to be congratulated on attempting such a task because you will graetly increase your knowledge through this activity.

I will provide the following comments re some of the statements made in the text and the posts. Unfortunately Fourier Analysis cannot be performed with calculus - it is an application of calculus. Also sound is not just voltage a quick review of a schematic for a power amplifier will often show parallel class AB stages - provided to give current gain following the voltage gain stages. An amplifier that only provides an outputvoltage but which cannot providecurrent will not drive a loudspeaker.

Decibels are a convenient ratio but they must be referenced to something to have an abolute magnitude - this is often forgotten it is okay when the people in the discussion now the context of the units but can be embarressing if they don't So while the equations are correct they need further explanation to illustrate: dBW is power relative to 1 watt in a 50 ohm load, dBm is power relative to 1milliwatt in a 50 ohm load. So a signal of 30 dBm is equal in power to a signal of 0 dBW i.e they are both 1 Watt in 50 ohms.

The best and most readable book I ever read on Fourier Analysis is by K.A. Stroud called Fourier Series and Harmonic Analysis which provides a great introduction to what is an extremely powerful mathematical tool.

Good luck with this it is quite the undertaking

 

[museav]

Re: %26quot%3BThe Electronics of Audio%26quot%3B

Decibels are a convenient ratio but they must be referenced to something to have an abolute magnitude - this is often forgotten it is okay when the people in the discussion now the context of the units but can be embarressing if they don't So while the equations are correct they need further explanation to illustrate: dBW is power relative to 1 watt in a 50 ohm load, dBm is power relative to 1milliwatt in a 50 ohm load. So a signal of 30 dBm is equal in power to a signal of 0 dBW i.e they are both 1 Watt in 50 ohms.

This is indeed a common oversight, decibels are a ratio and you can express relative levels to one another as dB without a reference but any absolute levels require defining a relationship to a standard reference. However, I believe the load is not necessarily part of the reference, for example my understanding is that dBW is simply relative to 1W and dBm to 1mW regardless of load while for dBu a specific load is defined (1mW into 600 Ohms). This is a problem many texts seem to experience, if you get into details you have to get them all right or it undermines the legitimacy, so sometimes it may be better to not get into them and potentially draw away from the primary message.

Also sound is not just voltage a quick review of a schematic for a power amplifier will often show parallel class AB stages - provided to give current gain following the voltage gain stages. An amplifier that only provides an outputvoltage but which cannot providecurrent will not drive a loudspeaker.

A valid point, but this is the kind of getting caught up in details that I think is great for advanced texts but diminishes the usefulness of many other texts. There are texts that get into the details of the different amplifier class topologies but few seem to just address the more general issues, such as that all an amplifier outputs without a load connected is voltage (there is no power without current flow and no current into an open circuit) and that the output with a load is voltage (greatly non-load dependent) and current (very load dependent). I've seen texts that go into details on the electronics but very few that simply address the basic concepts of why an amplifier may be rated 500W into 8 Ohms and 1,000W into 4 Ohms but only 1,500W into 2 Ohms (current limiting) or why you may still get the full rated output regardless of where the level control is set, although those are the issues that seem to most directly impact most systems and users.