Brüel & Kjær Paper on Phase Distortion, and the hi fi lottery

I am always interested in references to phase distortion – the distortion that is largely unknown and ignored by audiophiles. Here is a 1974 paper from no-nonsense audio measurements people people Brüel and Kjær. They say:

A poor phase response has no influence on the reproduction of pure sines; nor on steady state music, such as a sustained chord from an organ. But it shows up in transients, such as booms from kettle-drums, or bass drums, pizzicato from strings, short blasts from horns, attack on piano and guitar and the clash of snare drums, cymbals and triangles.

More specifically, phase-related distortion is not just an academic curiosity, but is an actual colouration:

If the boom from the kettledrum is considered under such a situation, it results in a coloration of the reproduced signal — too boomy if the bass arrives first at the ear; and too sharp if the mid frequencies arrive first.

Time-alignment of the drivers is key (conventionally performed by physically moving them backwards and forwards relative to each other), combined with the phase responses of the drivers and their crossover filters. And not forgetting that passive crossovers introduce other distortions (iron cored inductor saturation? poor driver damping? etc.) and that ported enclosures are responsible for other anomalies (see The Importance of Bass). With passive crossovers, more ‘ways’ = much more complexity, and they never quite work properly and sound bad in themselves. To avoid this, the fewest number of drivers possible are usually used, and the drivers may be required to work over excessively wide frequency ranges, responsible for cone breakup, beaming and doppler distortion.T

This whole thing is mind-boggling to me: there is no wonder that speaker designers tend to go on about what a difficult job they do and how it is an “art”. There are so many interacting variables that there must always be an element of trial-and-error, and much listening to the results in order to find the least worst compromise. Measurements cannot help much when everything is partly-wrong, and the aim is simply to find the least subjectively-offensive combination of errors.

Combined with standard-issue valve/vinyl audiophile equipment that contributes its own colourations, perhaps a particular colouration partly-masks another colouration when listening to a certain recording at a certain volume in a certain room with the speakers a certain distance from the wall toed in at a certain angle, using a particular type of valve amplifier with a particular transformer tap, playing from a particular cartridge set up with a particular tracking angle and a particular pressing of the LP that has been played a particular number of times previously. You get the picture. The number of permutations goes up exponentially with the number of variables, and with a conventional setup, each completely-subjective listening trial must take a minimum of several minutes to perform. No wonder passive speakers are a lottery.

On the other hand, it seems obvious that the DSP active version with digital source and solid state amplification, reduces the number of variables drastically and allows the designer to simply dial in something close to the optimal settings first time, for much lower cost. Some audiophiles may see this as taking away much of the ‘fun’ of hi fi, but once a price tag of thousands of pounds is attached to it, I think all “fun” has gone out of the window!

http://www.bksv.com/doc/17-198.pdf

Dynamic Compression – benign or evil?

I’m not talking about the ‘loudness wars’ and the way modern popular music is compressed to within an inch of its life, but merely what might pass as an ‘audiophile recording’, yet which will most likely have had a modicum of compression applied. This will have happened because it is conventional audio wisdom that the dynamic range of the real world has to be reduced in order to reproduce it on a hi fi system. Even classical recordings will generally have had some compression applied; replay systems that can reproduce a symphony concert at “realistic volume” are supposedly a myth.

I don’t agree that compression should be mandatory. For a start, I think that dynamic range is often confused with maximum volume level. Dynamic range per se is a fairly academic measure: effectively the ratio of the loudest and quietest levels in the recording. If it is a live recording, then the ‘noise floor’ is defined by wheezing, snuffling, shuffling, coughing, sweet wrapper rustling, chattering audience members. If not, it may just be the air conditioning and the involuntary vocalisations of the musicians (which seems to be quite a common problem). The dynamic range, as such, certainly isn’t going to trouble 16 bit audio. The maximum achievable level is a different issue.

From experience, sitting halfway back in a concert hall, a full symphony orchestra is not all that loud; I am confident that large speakers can reproduce the maximum level and the dynamic range in someone’s living room. (Clearly some people think that in order to do this, the speakers have to be the 50 piece orchestra – which of course would not be possible – rather than to merely reproduce the sound level as heard at a sensible distance.)

Small speakers, however, cannot reproduce a symphony orchestra or rock concert at a realistic ‘audience volume’ (- or at least not the full frequency spectrum) and people don’t always want to listen at high volume, anyway. The common technique of close-miking instruments tends to hardens the sound. Compression is usually assumed to have a benign effect that ‘takes the edge off’, allowing people to listen at moderate volumes without ‘the quietest bits’ dropping into inaudibility below the level of the microwave oven and washing machine. Dynamic compression is mandatory with vinyl because… well, for many reasons. Using it, it is still possible to perceive excitement, and the musicians playing loudly, even though the absolute increase of volume is small.

It never used to bother me, but it sometimes does, now. Thinking about it, why should something so drastic be completely benign, anyway? I can think of several weird things that it is doing:

  • The obvious thing is that it is continuously modulating the gain (duh!) and this has surely got to increase the work that the brain has to do in tracking what is going on. Sometimes individual elements in the mix will have their own compression applied, and sometimes it will be more like blanket compression that modulates several sources at the same time – just depending on who applied it and at what stage in the production.
  • The system pulls its punches on dynamics, denying the listener the sheer thrill of a great crescendo or the contrast of an unexpected ‘quiet bit’.
  • The strangest thing, I think, could be what it does to our perception of the frequency content of what we’re hearing. It partially neutralises the Fletcher Munson effect, meaning that we hear more of the bass and treble extremes in the quiet bits than we should, and are denied the full spectrum in the loud bits. Acoustic sources naturally change their frequency content as they are played harder, but with compression, we don’t get the full corresponding volume increase. It probably sounds like nonlinear distortion – another thing for our brains to cope with. In addition, the frequency content may be being explicitly modulated using a technique called multi-band compression.

Some classical labels pledge not to use dynamic compression, and they usually seem to include more ‘ambience’ than other recordings i.e. are not miked so closely. In my experience they can sound amazing. However, they must be played back at ‘realistic’ volume – not a great drawback in my opinion!

Rival Sons, on Later with Jools

A great band.

It’s always worth watching Jools Holland’s programme to catch this sort of thing. I like their style, and the way the keyboard fills out the sound, avoiding the out-and-out abrasiveness that guitar and vocals-only can sometimes generate.

The production does a great job of conveying the impression that this was loud!

I love it, but does this sort of thing appeal to today’s typical S.A.F.F.Y.?

Digital Audio was a Beautiful Idea

Reading a little of the history of the development of digital audio, it is evident that the recording industry in the 1970s had reached a point where analogue technology was a bottleneck preventing truly transparent recording and reproduction. Experimental digital machines were introduced tentatively, in parallel with analogue systems during classical recordings, and from the off it was clear to the labels that digital was the way of the future. Initially, of course, the digital recordings were distributed to the listeners via vinyl, but the introduction of CD allowed them to be heard in people’s homes exactly as they were in the studio. Digital versions of many of the 1970s digital masters are available even now, and sound perfectly fine – as the recording professionals knew at the time.

With digital, not only is the quality orders of magnitude higher than analogue on any measure, but the ‘perfect’ source is now a chip that costs pence and requires no maintenance. Its job is to be transparent and contribute no sound of its own, and it does this admirably.

However, I do not think that the majority of audiophiles share my certainty of the superiority of digital audio for serious listening. They may tolerate their CD player, or a streamer and a DAC, but in their heart of hearts what they really love, or would aspire to own, is a turntable. In my world, audiophiles (and I think I am one in my own way) are rare. It is a disappointment to me that the ones that I do know, invariably wish to talk about vinyl and its attendant paraphernalia. “It’s OK, but not as good as vinyl, obviously.” said one, when describing his digital-only system. As an ‘ideas person’ (and I think I am one, in my own way) I actually find this offends me, and I have the urge to argue with them, but it would be futile I know.

The beautiful idea and its practical realisation have made it as far as becoming a medium for the masses, and the quality of digital audio has hitherto never been doubted by classical music enthusiasts. But the power of superstition, placebo and expectation bias was never going to allow audiophiles to be content.

A number of forces have aligned to create a ‘vinyl resurgence’.

  • Simple psychology that cannot square the circle of beautiful art being embodied within numbers and plastic chips
  • The need for a physical prop or totem when listening to music.
  • That the ‘loudness wars’, over-compressed MP3s and digital downloads all became ubiquitous at the same time, tarring all digital audio with the same poor quality brush.
  • A sense that modern life is soulless and that digital technology is partly to blame.
  • ‘Hipster’ fashions that include old instamatic cameras, and now vintage audio gear.
  • Falling record sales and the music labels looking for higher margins and another way to encourage people to buy their music collections again. Again.

Some classical labels are considering releasing music on vinyl once more. Many bands now release LPs in parallel with digital downloads and CDs. Will the digital versions therefore also be compromised in the ways that are necessary to squeeze music onto vinyl? Or worse, will there be deliberate nobbling of the digital version in order to justify the high prices of the vinyl product? Not many people realise that ‘vinylisation’ isn’t just a bit of judicious compression or ‘de-essing’ of the digital master, but could also involve compromises at the recording stage itself – so we digital audio consumers may be affected by the vinyl fad whether we like it or not.

It’s a mini-tragedy that a perfect idea came along, democratising high quality audio in the process, but that it has then been tarnished through superstition and ignorance. Even those people who were, and are, happy with digital audio are under a constant media onslaught of articles implying they are tin-eared philistines without souls. Some of them will cave in, and buy turntables. Ultimately they will be dissatisfied with the sound, always worrying about dust, belt stretch, stylus alignment, and aware that the record is damaged a little bit more each time they play it. If only they could have been allowed to enjoy the logical conclusion of the digital audio concept: the streaming audio service that makes all of the world’s music available at the press of a button, in perfect quality – as is just around the corner. Audiophiles were given the keys to the sweet shop, but decided to stay outside gnawing on a bit of celery.

Of course digital audio will remain the dominant medium for distribution of 99% of music, but all the movers and shakers in the industry and their most influential, affluent customers now despise it! I think that the originators of digital audio cared passionately about what they were doing, but there are few remaining who remember that it was primarily about quality and not mere convenience.

Preferences?

I commented on an article about psychoacoustics the other day, and found myself making an argument that, while it seems perfectly logical to me, I don’t think I have seen anyone else make before. Basically I said that if I have a system that is as ‘correct’ as I can make it, and I don’t like the sound, then changing the system to something that I know is ‘less correct’ is not going to help. While I am, in fact, confident that I will like the sound of a ‘correct’ system, it highlighted an issue that I had not thought through fully before: the idea that it is everyone’s duty to keep tweaking a system until it meets their own personal “preferences”.

Is this not where most audiophile woes stem from? Whether or not a person’s preferences are ascertained ‘scientifically’ using the sanctified method of double blind testing, is it not a road to misery and impoverishment? In this scenario there is no ‘stake in the ground’; everything is fluid and shifting and the afflicted audiophile can never be sure whether his hearing is at fault or if it is his personal choice of ‘musical’ components, quirks of the recordings, the weather, or a lack of coffee.

While many people could conceive of applying the “they all sound the same” argument to a DAC or a solid state amplifier, they would not believe that it was possible to apply it to the whole system. The reason why it might seem so strange is that they’ve never heard anything resembling a ‘correct’ system in the first place (I suggest active crossover, phase correction, sealed woofers, unrestricted bass) but they have been led to believe that the systems they have heard were ‘high end’ – yet they all sounded different from each other.

Where are the Tunes?

If I think about it, I have always made some pretty simple assumptions on how musical tastes vary across demographic groups (rather as Lauren Laverne did in the very watchable series Oh You Pretty Things). Recently, though, I have gained the impression that young people’s tastes are not quite how I would logically have imagined them to be.

I have always assumed more-or-less the following:

  • When we are children we can only engage with elementary, simple melodies and rhythms, just as visually we prefer cartoons to more sophisticated material.
  • As we get older, our taste and sophistication gradually develops, enhanced and directed by education and our circumstances.
  • Despite our parents’ dismissal of ‘our’ music as “just noise” much of it is/was nothing of the sort. We all enjoy a good tune and a repetitive rhythm, whether we like to admit it or not (or so I thought). Tracks that meet that description vary greatly. I remain underwhelmed by The Undertones, for example, but they were officially brilliant – John Peel said so. Music that appeals to children and teenagers can still appeal to old age pensioners; The Beatles, obviously.
  • Writing a simple, satisfying tune is more difficult, if anything, than writing ostensibly-sophisticated twiddly music.
  • In our teenage years we may develop a taste for ‘excess’, that is, music that is a sort of parody of itself, be it punk, death metal or rap. Some people never move on from this!
  • For most people their peak of engagement with music occurs somewhere around the age of 20-25, and in many cases never develops from there – the musical taste of most people of my acquaintance (aged around 50) ossified circa 1986.
  • I have never been entirely convinced that some people, including myself, are immune from pretentiousness or cultivating an interest in certain types of music in order to impress other people – which muddies the waters when trying to understand people’s tastes at the more sophisticated end of the spectrum.

Logically, a person who apparently develops a taste for abstract modernist classical or musique concrète etc. should be educated, sopisticated and of a certain age, having become bored over the years with the simplicity and predictability of melody, and is craving stronger flavours. But, how could a 20 year old be in that position? I have always assumed that if such people existed, it was, perhaps, because they were interested in music as an intellectual exercise rather than listening to it in the same way as the rest of us – and that goes for the composers as well as the audience. In other words I decided that these people were outliers that didn’t fit the general ‘theory’.

But in that case, how can I explain this?

…and many others like it. It’s certainly not Love me Do is it?!

Many of today’s young people seem to be sublimating directly from predictable teenage fare and straight into full-fat modernism or musique concrète! There is no excess, no obvious melody, nor even any repetitive rhythm. This does not fit my theories at all. What’s going on?