Friday, December 15, 2017

Limiters, Compressors, and how to play music loud


The excessive volume of commercials has struck everyone who’s watched television.  You’re watching a show at a comfortable volume, and there’s a commercial break, and suddenly you are blasted out of your seat.  If you had the volume on 5 it feels like it just went up to 100, all by itself.  How does that happen?

I was reminded of that question when reading a new book - Damon Krukowski’s The New Analog – Listening and Reconnecting in a Digital World.  The book tackles that question in the context of the transition from analog to digital audio and television.  Younger readers may not remember that transition (it was a process, not a single event) but all of us who were adults in the 1980s lived through it not once but many times.

Journey in concert (c) John E Robison

First there was the transition from vinyl records (analog) to compact discs (digital.)  Then the audio processing went digital, with smartphone apps replacing sound processors and digital Bluetooth links replacing analog headphone cords.    Call phones started as analog and now are all digital, and far more capable for the change.

But interestingly, it’s not digital technology that allows those commercials to blast us.  That is an old analog trick that came from the radio broadcast world seventy-plus years ago.

In his book Krukowski shows waveform samples from two versions of a popular song, showing how one version has “normal” dynamic range and the “loud” version has everything pressed to the maximum.  Any listener would say the second version is louder than the first, but an engineer would point out that the peak energy in both programs is the same. 

Krukowski explains that everything was turned up, but maximum volume remained the same, so that the soft passages got louder and the loud passages all became 100%, or full volume.  What he does not explain is how that happened without the music getting horribly distorted.

Building upon his excellent book I’d like to offer that missing explanation. The answer to how music got louder is compression and limiting, two technologies that existed for a long time but which were enhanced dramatically in the 1970s.

I designed compression and limiting systems when I worked as an audio engineer.  Limiters were originally developed for radio broadcasting, where too much program volume corrupted the radio transmission.  Limiters prevented that by turning the program down automatically if the radio announcer got too exuberant.

Limiters operate by measuring the peak level of a program and turning down volume when a preset threshold is exceeded.  If the limiting threshold is set below the level a sound system can deliver cleanly, the system will in principle always be clean.

As concert sound systems grew larger in the 1970s sound engineers realized something else.  When amplifiers are driven beyond full power the output waveform is “clipped” at the maximum level the system can deliver.  Clipping turns a smooth musical wave into a harsh square wave.  Listeners know this clipping as “fuzz,” a sound effect that remains popular today.  When one instrument is clipped the effect sounds purposeful.  When the whole musical program is clipped, the whole program sounds bad. 

Sound quality is not the only casualty when amplifiers clip.  Clipping is also destructive to speakers. In fact, most concert speaker failures are traceable to excessive clipping.  Horn drivers are prone to shatter and voice coils in speakers overheat and deform.

In 1978 I spent the whole of April Wine’s FirstGlance tour replacing speaker diaphragms after they shattered from the lack of limiters in Pink Floyd’s Britannia Row rental sound system.  It was that tour that showed us the need for limiters on each of the amplifier banks in a multi-way system.

April Wine - First Glance tour plans  photo (c) John E Robison

Limiters prevent that by keeping amplifiers from breaking into their clip or overload region.  When a limiter is triggering occasionally it’s said to be “peak limiting” which is an acoustically transparent thing.  The only thing listeners notice is the absence of clip distortion. 

If the program level is raised as the limit threshold is lowered the limiter begins operating all the time, as opposed to only during loud passages.  When a limiter is used in that way it’s called a compressor because it’s reducing the dynamic range (ratio of loud to soft parts) of the program. 

Limiters are usually set up with “hard” limits, meaning material that exceeds their limit threshold are reduced in overall volume to stay under the threshold level. 

Compressors, on the other hand, have “soft” limits, meaning signals that exceed the threshold are limited, but in ratio.  So a burst that exceeds the limit threshold by 50% might be limited to just 25% increase at the output. 

Soft limits reduce dynamic range without limiting peak volume so they still allow amplifiers to go into clip distortion (and radio stations to overload.) Consequently they are not seen in those applications.  Hard limiting is the rule there.  Soft limiting is used when producers want to compress the dynamic range of a music program; for example to make it more audible in a crowded area, or to make it seem louder at a given volume setting.

Soft limiting for compression followed by hard limiting for overload protection is the technique that delivers maximum average sound levels in live performance and the loudest program on playback.

Lower frequencies (bass) use most of the power in a concert sound system so the bass speakers are usually driven by separate amplifiers.  For maximum volume we applied separate limiters to the bass amps and the higher frequency amps.   As volume rose, the bass would be heavily limited even as the highs remained untouched, with their full dynamic range.  That bass limiting made for a very solid steady foundation that became part of the characteristic sound of the disco/soul/funk era.

While some musicians used limiting or compression as an effect on individual instruments it was mostly a tool to get more reliability and volume from house sound systems.  As far as I know that remains true today.

The main difference between limiters and compressors of the 1970s and the units in use today is that the sound signals are now digital, and compression/limiting is done in software rather than by purpose-built circuits.

Digital limiting allows for a range of options that could not be accomplished with analog circuits, particularly in the studio. For example, digital compression software can evaluate a whole song and apply smoother compression and limiting by looking ahead and behind the peaks before calculating adjustments. 


The main tradeoff of digital limiting is that it takes time to do the calculations, and the application of limiting contributes a few milliseconds of delay to the signal flow.  Some musicians are bothered by that latency if they hear the house sound system on stage.   Others won’t notice, or will ignore it as they ignore natural hall echoes and delays.  Analog limiters don't have delays.

When you hear music or commercials that are far louder than you expect on the radio or tv, you can thank limiting and compression for it.  When you hear LOUD on a concert stage, it's limiting, compression, and possibly just a shitload of horsepower in the amplifiers.

John Elder Robison



John Elder Robison is an autistic adult and advocate for people with neurological differences.  He's the author of Look Me in the Eye, Be Different, Raising Cubby, and Switched On. He serves on the Interagency Autism Coordinating Committee of the US Dept of Health and Human Services and many other autism-related boards. He's co-founder of the TCS Auto Program (A school for teens with developmental challenges) and he’s the Neurodiversity Scholar in Residence at the College of William and Mary in Williamsburg, Virginia and a visiting professor of practice at Bay Path University in Longmeadow, Massachusetts.  

The opinions expressed here are his own.  There is no warranty expressed or implied.  While reading this essay will give you food for thought, actually printing and eating it may make you sick. 


Friday, December 8, 2017

Modern cars have standard machine readable vehicle identification (VIN) numbers.  Old cars have numbering methods that vary from one brand to the next.  In this essay I will show you what numbers look like on Rolls-Royce and Bentley motorcars from the 1970s Shadow through the 1990s Spur era

This article is illustrated with images of a 1983 Rolls-Royce and a 1990 Bentley.  The 1983 car is a Corniche Drophead; the 1990 is a Continental Convertible



The number plate most people know is in the driver door jamb - the area of body in front of the front door.  You should see a small plate that identifies the model (Continental in this example) and a larger plate with the date of manufacture and gross vehicle weight (the maximum the car can weigh, fully loaded) and the gross axle weights (the maximum weight on each axle, fully loaded.)

The large plate has the vehicle identification number and say the car meets requirements for whatever market for which it was originally built.  The photo here shows a US market car but other markets are similar.



Cars built after 1987 should have bar code tags with a machine readable version of the VIN at the rear edge of the doors, as shown below:



You should see a metal plate with the VIN at the base or side edge of the windshield:




If you open the hood (bonnet) you will see a body number plate on the firewall.  This shows the body number, which is the fourth digit of the VIN, and the last 7 digits.  Reading the plate below you can see how the body number is derived from the whole VIN, shown in the photos above at the windshield base.




The plate on the left underside face of the bonnet (hood) gives the paint and interior trim codes.  Some cars will have one code; two-tone vehicles will have two.





The VIN is also stamped into a structural part of the body on or adjacent to the right front strut tower or wheel well, as shown below.  Newer cars will have a bar code VIN tag on the strut tower also.







Here is an excellent article on decoding Rolls-Royce and Bentley numbers.

Here is an earlier article on chassis and engine serial numbers, using a 1972 car as example.  This is on the Robison Service blog also


© 2017 John Elder Robison

John Elder Robison is the general manager of J E Robison Service Company, celebrating 30 years of independent Bentley, Rolls-Royce, BMW/MINI, Mercedes, and Land Rover restoration and repair in Springfield, Massachusetts.  John is a longtime technical consultant to the car clubs, and he’s owned and restored many fine British and German motorcars.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

Reading this article will make you smarter, especially when it comes to car stuff.  So it's good for you.  But don't take that too far - printing and eating it will probably make you sick. 












Sunday, December 3, 2017

Thoughts on To Siri With Love



I just finished a controversial new book, To Siri With Love by Judith Newman. Reading this book made me feel like memoirs from autism moms are a thing whose time has come and gone . . .
At the same time, I can’t help but believe the publisher who brought this story to market, and the reviewers who praised it, must not share that opinion.  And of course the author does not seem to hold that opinion either.  I’ve no doubt she loves her autistic son and wants the best for him. 

So why do I find this book troubling, even as the non-autistic literary community has lavished praise upon it?  And lest you think it’s just me that is troubled . . . the reason I read the book was the storm of tweets and messages I received from autistic people urging me to boycott or criticize it.

Perhaps this is an autistic thing. Maybe it's a situation where non-autistics find a story about one of our tribe interesting or entertaining, even as we autistics find the same words deeply troubling.

Without giving it all away, I’d say the author’s attitudes toward her son, her family, and autism appear to be at odds with the set of values and ideals that is taking shape among autistic self advocates today.  It would be a great understatement to say the author’s views would be aggressively challenged by, for example, the neurodiversity students at a university like my own William & Mary.

As expressed in the book, the author’s ideas triggered many autistic readers (including yours truly) to such an extent that the book’s other messages were missed. For example, the premise of the title - that a young autistic fellow could find a friend in Apple’s Siri seems largely lost.  Little is made of the relationship between Gus – the autistic star of the book – and Siri other than to dismiss it for shallowness and nonhuman nature.

I found that ironic as I’d written a chapter “One With The Machine,” in Look Me in the Eye. In that I describe talking to and becoming part of a concert lighting system.  Not one of the million-plus people who read that story called it shallow.  If I could talk to lighting, why can’t Gus talk to Siri?

It’s not for me to answer, but I’d speculate that the mom may not understand that aspect of her son, and she dismisses what she doesn’t get.  I don’t know her, but I know that is a common human trait and I’ve known other people who would behave exactly that way.

The tone of the book left me feeling uncomfortable in many spots. I had that feeling when the author talked about her non-autistic son (musing about masturbation), her husband (who made her suffer through endless monologues about the subway, which she says she tolerated so he wouldn’t inflict them on someone else) and her autistic son Gus (for whom she wishes to remain adult guardian in case she needs to regulate his reproductive ability.)

That last bit was particularly disturbing to many autistic readers.  Her description of Gus is that of a sweet, kind teenager who thinks and talks, and gains more skills with every passing year.  Guardianship law mandates that people with developmental challenges be given the maximum amount of self-determination, which seems opposite her stated goal.  If I were Gus and I read that, I would run away tomorrow and take my chances on the street. 

Now, the author may feel that's irrelevant because her son won't read it and react that way, but putting her son aside, I'm surprised she did not consider how badly another autistic person might react to those words.  They clearly position her writing as from a non-autistic parent's perspective and embodies much of what actual autistic people criticize in such literature.

Early in the book Newman implies her  son is not fully sentient. She asks why she is unable to find anything she can share with him.  Yet her descriptions paint a picture of a boy with many interests (which she must not share) and enough thoughts that sentience should not be in doubt.  A thoughtful reader is left to wonder how much of the book's reflection on the child actually bears upon the mom?

There are other characterizations that may be unintentional but which were still deeply offensive to the subjects.  For example, autistic creative person Amythest Schaber was described as “looking like everyone’s favorite manic pixie dream girl.”  I can’t speak for Amythest, but I can assure you that I’d be upset if someone introduced me that way.  What does it matter what someone looks like, if the purpose of discussion is their insights?
  
If you are writing a nice, funny, or helpful family memoir there is a good test authors should use:  Would the child subjects of the book be humiliated if they read the story as an adult?  In my opinion this book fails that test. It says things I would not write about my own kids, had they done those same things.

Ten years ago when I wrote Look Me in the Eye there were a ton of autism mom blogs describing family behaviors in similarly embarrassing detail.  I wondered about that at the time, thinking how upset I’d be to read such about me.  Thankfully many of those stories have since been taken down or edited. 

With respect to Siri With Love, I will just say that if Gus reads it, I hope he believes his mom does have great love for him just the way he is and will be.

With all the talk of Gus’s disability and how (in his mother’s stated opinion) he may not amount to much on many fronts, one thing comes through loud and clear:  Gus does not seem to feel disabled at all.  He’s a pretty happy guy, content with life.  As she says, Gus is not self injurious angry or destructive.

Might that be just enough?  Or if the author wanted more, might she direct herself toward helping develop a safe secure housing plan for Gus if and when he requires lifelong supports, knowing she will be gone?  I did not see much of that in the story, yet that is many parent's biggest concern.  Gus's challenges are no doubt real and significant.  I get that much from the story. My issue is with the attitude, which just did not make me feel good.  

I’m an autistic guy, and a parent of an autistic son whose mom also was (she died a few years ago) autistic. I’m the son of an autistic dad, so I’ve got autism covered all ways.  Even so, I realize autistic people come in all shapes, sizes and viewpoints and some are rather divergent from my own.  I’ve little doubt that Judith Newman loves her son and had the best of intent writing this book, and I feel bad for penning what feels like a relentlessly negative review of her work.

I hope my words help her to understand why her book has elicited the strong response she’s getting from some in the autism community, and set her on a path to reconsidering some of her views in light of the thoughts emerging from actual autistic people.  Ms. Newman is clearly a talented writer and I expect we will hear more from her in the future.  I certainly hope I can paint a more positive picture of her next work.

There were many spots where this book made me uncomfortable as I saw myself in the narrative.  The husband’s monologues – I’m like him today.  Gus’s obliviousness to some things – I’m still the same now.  In both cases I would very much hope my own wife or mother did not feel as she wrote.

If this book shows one thing it is this:  Parents need to hear about autism from actual autistic people.  Parents need support too, but the place to get that is in private, not by discussing our(their) kids in a public forum. 

Always remember that the only people who truly know what it’s like to “live autistic” are actual autistic people.  Everyone else is watching and guessing, sometimes correctly, but other times . . . disastrously wrongly.

John Elder Robison


John Elder Robison is an autistic adult and advocate for people with neurological differences.  He's the author of Look Me in the Eye, Be Different, Raising Cubby, and Switched On. He serves on the Interagency Autism Coordinating Committee of the US Dept of Health and Human Services and many other autism-related boards. He's co-founder of the TCS Auto Program (A school for teens with developmental challenges) and he’s the Neurodiversity Scholar in Residence at the College of William and Mary in Williamsburg, Virginia and a visiting professor of practice at Bay Path University in Longmeadow, Massachusetts.  

The opinions expressed here are his own.  There is no warranty expressed or implied.  While reading this essay will give you food for thought, actually printing and eating it may make you sick. 


Monday, November 13, 2017

If you could change autism research today, what would you do?



Recently I suggested that people who are actually autistic need to have a strong voice in guiding autism research.  I made the point that anyone who is not autistic is simply guessing when it comes to interpreting our behaviors.  Only an autistic person can truly know autistic life.  That is not a slight against parents; it is just reality.

Some autistic people are parents too, and they have both perspectives.  That’s particularly valuable.  And parents as a group are the only ones who can report fully on the development of very young children who can’t speak for themselves.

But it leaves a fundamental question unanswered.  If I believe autistic people should have a strong voice in guiding research, what would I ask for?

Autism is a difference that affects us through the lifespan.  Childhood is 20-25% of the typical lifespan.  Less than 5% of current research is directed toward understanding adult issues.  I would shoot for 50% of newly funded research addressing at either adult or full lifespan issues.

I’d require that proposed research include a statement from autistic community members about the methodology, utility, and ethics of the proposed study.  I’d expect at least half the community members to be actual autistic people with the others being parents and professionals.

As for the topics of study . . .

I’d make the study of apparent early mortality of autistic people a top priority.  Why does it happen and what can we do?

The initial findings on suicide and suicidal ideation are scary enough that I think that area deserves its own concentration of study.

I’d put considerably more emphasis on understanding the co-occurring conditions that accompany autism.  Epilepsy, anxiety, intestinal issues, depression, and others.  Most of these conditions seem more resistant to treatment or control in autistic people.  Why is that and what can we do?  If we could control or remediate these symptoms we’d be a lot closer to minimizing autistic disability.

Look at epilepsy in the general population.  Successful management via meds means no seizures.  Now look at many autistics - same meds every day, but seizures still happen.  Poor control.  Or take depression.  Autistic and non autistic mostly manage with meds.  Yet we autistics are nine times more likely to kill ourselves.   Why are our outcomes so much worse?

Many autistic people have sleep problems.  That is another co occurring condition that merits more study.  The number of problems associated with these co-occcurring conditions make me think that a large fraction of the pain and suffering we autistics experience comes from those things, and if we could relieve that it would be a really big deal.

I’d encourage research aimed at improving communication skills, both verbal and non verbal.  We've funded programs like PEERS and UNSTUCK to tremendous benefit.  

I’d encourage research into improving executive function for autistic people at all levels of support.

I’d figure out how to expand apprenticeship/work training programs like Project Search that can transition both low and high support autistic people into the workforce.  These projects have shown very encouraging results but we don’t know how to replicate them widely.

I’d seek research proposals from engineering and industrial design people looking for innovative solutions to help non speaking autistics communicate.  We have letter and symbol boards, and ipad versions of same, but I think there is a lot more potential there.  Unlocking communication is the biggest thing we could do to relieve disability in some people.

I’d study other ways technology could be used to minimize our autistic disabilities.  We think of autism as something we’ll address through medical treatment or behavioral therapy but there is tremendous promise for help through engineering.

I’d study the housing options for adults who cannot live independently.  Sharp differences exist between supporters of community and individual apartment housing.  We should agree that we need safe, supportive, affordable housing options that parents can trust when they can no longer care for higher support adult children at home.

I’d figure out how to extend the supports given to autistic people through high school into adulthood.

I’d tackle the pressing questions the IACC has collectively identified in the 2017 Strategic Plan Update.

Finally, I’d ask the community what their concerns are and synthesize them into a revised plan.


This is far from a complete list, but it’s a start

John Elder Robison


John Elder Robison is an autistic adult and advocate for people with neurological differences.  He's the author of Look Me in the Eye, Be Different, Raising Cubby, and Switched On. He serves on the Interagency Autism Coordinating Committee of the US Dept of Health and Human Services and many other autism-related boards. He's co-founder of the TCS Auto Program (A school for teens with developmental challenges) and he’s the Neurodiversity Scholar in Residence at the College of William and Mary in Williamsburg, Virginia and a visiting professor of practice at Bay Path University in Longmeadow, Massachusetts.  

The opinions expressed here are his own.  There is no warranty expressed or implied.  While reading this essay will give you food for thought, actually printing and eating it may make you sick.