Distortion Emulation and Results

Skip down to the observations if you just want to see what I heard.

Recently I have been doing listening tests on the effects of distortion by processing sound to emulate a system. I have tried different combinations of crossover frequencies (or full-range drivers), amplifier/driver types (specifically their overload characteristics and power limitations). The way I do this is split the audio into tracks representing each driver (e.g. tweeter gets 900hz+, woofer gets 90-900, sub gets <90hz) depending on setup, then I set the parameters on each track to model the amplifier/driver system.

For example, a conventional woofer's response curve drops faster and faster as the coil extends away from the magnetic gap (xmax being measured where the field strength is equal to 70%, in most cases), so increasing the voltage or lowering the frequency will cause a non-linear increase in cone excursion until either the amplifier runs out of power or the driver reaches its mechanical (bottoming out) limits. The system might also include the effects of a crossover and another driver powered by the same amplifier; there might also be an EQ, compressor, or limiter (especially on subwoofers or in high-power commercial applications where driver protection is a must).

A mathematical algorithm which represents the system is entered into the engine which calculates each sample value based on its current value and the values of those samples around it. The result is the waveform as would theoretically be measured in a nearfield test of the driver under the same conditions in a practical test. The result from each driver is mixed back together into the full spectrum which is played back through my calibrated system at a level well within the distortion limits of my system, allowing me to have an idea of what different combinations might actually sound like.

I understand that it is crude to listen to the results through speakers with their own issues (crossovers, specifically), but it really does give me a good idea of what certain conditions might sound like WITHOUT damaging my ears or system.

---The models are somewhat crude and do not include effects such as cone break-up, driver ringing, or enclosure type.. The effects of these details are likely lost by listening through a speaker system in the first place.

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Most of the test tracks were from Tool's Lateralus, an album I believe has very good sound quality suitable for such testing.

Observations (most of which are logical, known, and/or expected):

-An overloaded bass driver will cause distortion that covers up details in the mid-range regardless of crossover frequency, although lower crossover frequencies will reduce the severity of the masking since less of the signal is being distorted by the affected driver.

-An overloaded bass driver will cause the sound to be harsh due to shifting of the spectrum toward the high end, all caused by a continuing increase in the intensity of higher-frequency drivers while the bass driver has reached its output limits.

-Using a compressor or limiter on the bass portion of the spectrum will minimize the mid-range masking and distortion by keeping the driver within its linear region; however, the output of the bass driver will be limited slightly, causing the sound to become harsh at a lower overall level (bad), albeit with unmasked mid-range detail (good).

-Bi-amplification is synergistic. Two 50-watt amplifiers spread across a multi-way speaker will give more headroom than a single 100-watt unit, more so with Tool than the other test tracks I used. However, 3dB of headroom is lost for pure sine waves (which is not an issue considering that most music contains many frequencies at once).

-Use of a dedicated driver/amplifier (subwoofer) for the bottom frequencies (below 150hz) increases headroom and greatly decreases mid-range masking (good).

-As frequency increases, less power is used, but the peak levels remain the same. Higher frequencies are more dynamic, but have a higher crest factor. With all of the Tool tracks I tested, 2khz+ had the same peak level as sub-100hz. In fact, at some points the high-frequency energy peaked 6dB higher than low (specifically when there's a bass or palm-muted guitar played along with toms). This is a result of the "quiet intensity" characteristic of Tool.

-It definitely sounds better to have excess amplifier power pushing a driver into its non-linear region rather than under-powering the driver, causing harsh distortion.

-In all cases, using compressors or limiters, especially in combination with EQ (i.e. using limiting to keep boosted frequencies from over-loading), dramatically increases the maximum drive level before harmonic distortion or masking is heard, although dynamics are still reduced when peaks are limited.

-All processing can cause phase issues which don't sound good. A bit of correction fixes this.

That's all I have to say for now, mammoth post as usual. There's a lot more, but I'm not really in the mood to elaborate at the moment.

Aha. I tend to dabble in things I already know.

Efficiency, efficiency, efficiency. I keep thinking there has to be some completely different approach (missing the forest for the trees, lost in the details). I simply don't have the experience and understanding of circuitry and systems (including the room and psychoacoustics) to elaborate.

The end goal being to optimize the storytelling, captivation, and entertainment of the media such systems present, I keep noticing something's not quite right (both tube and solid-state, horn and conventional, etc.) with every system I've heard. Unfortunately divergent and innovative thought is hard to come by, making it difficult to see clearly.

I don't know.

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"Aha. I tend to dabble in things I already know."


Well, that keeps us comfortable, doesn't it? You get to affirm your own abilities, which is always of some comfort. However, if as a musician you only played those parts you already know you can accomplish, you would never move forward as a performer. Your playing would eventually get very stale and non-inventive before you finally got bored with the whole thing and moved on. That would be fine if that is what is meant to be in your life. There are many things I engaged in when I was young and had fewer responsibilities eating at my time committment which I no longer even much think about. I was not lacking talent in those areas or ability to acccomplish what I set out to do. But life got in the way and they eventually went by the wayside. If this is what you feel you need to devote time to, just as with practicing your music, make going over those things you already know - already have affirmed - only a small portion of what you do each day. Practice until you can do the task well and then move forward. If you don't have a direction in which to go, find someone who can provide a path.

http://www.quotes-daily.com/2010/08/overflowing-cup-of-tea-zen-koan.html

http://www.youtube.com/watch?v=h3xEHigWShM


"Efficiency, efficiency, efficiency. I keep thinking there has to be some completely different approach (missing the forest for the trees, lost in the details). I simply don't have the experience and understanding of circuitry and systems (including the room and psychoacoustics) to elaborate."


OK, you seem to at least have a grasp of all that you might need to know, particularly in someone your age. That's a very good sign in itself, Andre. The rather stupifying time comes for many people when they have acquired sufficient amounts of knowledge to actually grasp the entirity of all there is to know and how little of it they truly understand and have tiime in a single lifespan to attain. Let's go back to music again for an example from my own life. I played guitar when I was your age and though I wouldn't have ever called myself a gifted musician as far as technique was concerned, I was a talented player in many ways. Once again, life intervened and I sat the instrument down for a few decades - not an uncommon story if you read the guitar forums. When I picked the guitar up to play again I began self teaching myself as I knew the basics well enough to not need an instructor who wasted time getting me through chord progressions. I already knew enough to understand how much more there was to know. By self teaching myself I tended to have no great focus for quite awhile as I bounced from this style to that style and that method of approaching the fretboard to another. Not to say what worked for me is what will always work for someone else, but my playing only began to really noticeably improve when I said this is what I want to play and this is how I want to play that genre. To do that I need to understand and master what I could grasp as "this" amount of knowledge before I could move forward. So I would - from a very distant relationship with your forum posts - advise you to focus your learning more than you seem to be doing. Stop waiting for the big inspirational moment to come to you. Do a search for how many versions of the light bulb Edison created before he had a working model. If you want inspiration from afar, dive into Tesla.


Audio is very difficult due to the many fields in which you need suficient amounts of knowledge to continue your forward momentum. While I have always admitted to not being an engineer or a designer, when I was selling audio I worked with many people who were simply filling space on the salesfloor. I was the person they came to when they needed to repeat a spec for a customer or to have a circuit or technical concept explained. Those things were at first all in my head and I could call them up at will. Then, as the amount of information steadily grew beyond the space allotted for "audio" in my mental filing system, I finally realized I didn't have to know everything instantly. What I needed was a system which enabled me to find what I needed to know, when I needed to know it. Life became much simpler with more time to devote to things other than reading audio mumbo jumbo and I have accumulated a file of information I refer back to til this day with some amount of humor at what a few people thought was important in their day. But, overall, it's a good reference system and it has served me well throughout the last five decades.


"The end goal being to optimize the storytelling, captivation, and entertainment of the media such systems present, I keep noticing something's not quite right (both tube and solid-state, horn and conventional, etc.) with every system I've heard. Unfortunately divergent and innovative thought is hard to come by, making it difficult to see clearly."


Maybe you should stop being so critical of what is wrong with everything you hear. I've sold to people such as you are describing, Andre. They are a PITA! Why? Because, for the most part, they miss what is important in the experience. They are so d*mn busy being hyper critical of all the technical aspects of what everyone agrees is a still highly flawed playback system that they fail to perceive those things that are right about the connection with the music. They argue distortion percentages while I want to hear the oboe. They become obssessed with phase shift while I want to be drawn into the performance. I'm not saying those things they hear aren't important, but begin to listen for what is right and what is remarkably good about what you are perceiving. And don't always feel the need to quantify what you hear. Crritcal listening is a tool and, as with all other tools, it should only be taken out when it is appropriate for the job. Not every job requires a hammer.

For the most part, and this is from my experience only, US engineers are the only people who obssess over such things - they and the engineers who build equipment specifically to sell to them. The Europeans - for the most part - explore the experience of the event more than we do and their equipment shows where their emphasis is placed. Equipment coming out of France, Italy, Spain and Greece has a distinct personality that is lacking in American audio. The Japanese audio markets are bi-polar when it comes to equipment. There is a segment of the Japanese buying public which can become too overly involved in the intricacies of measurements and there is still the vital sub-market which reveres a vintage McIntosh or Marantz amplifier for how its circuits are laid out and where the wires are placed. The Japanese are the listeners who can be held responsible for the revived interest in direct heated triodes and horn loaded drivers. They hear the magic in the music and they focus not so much on what measurements can get them there but on why, when they hear such wonderful music, do their measurements not provide consistent guidelines for how to repeat the experience. There's little time left to devote to re-measuring what they already know they have measured.

I think you need a mentor, Andre, but I have often found the ultimate goal of an engineering education is to drive all of the curiousity out of a young mind. Those who insist upon remaining curious after they have received their degree are often ostracized as whackos.

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