A very enjoyable programme.
A very enjoyable programme.
Here’s a fascinating speaker:
It uses many transducers arranged in a specific curve, driven in parallel and with ‘shading’ i.e. graduated volume settings along the curve, to reduce vertical dispersion but maintain wide dispersion in the horizontal. I can see how this might appear quite appealing for use in a non-ideal room with low ceilings or whatever.
It is a variation on the phased array concept, where the outputs of many transducers combine to produce a directional beam. It is effectively relying on differing path lengths from the different transducers producing phase cancellation or reinforcement in the air at different angles as you move off axis. All the individual wavefronts sum correctly at the listener’s ear to reproduce the signal accurately.
At a smaller scale, a single transducer of finite size can be thought of as many small transducers being driven simultaneously. At high frequencies (as the wavelengths being reproduced become short compared to the diameter of the transducer) differing path lengths from various parts of the transducer combine in the air to cause phase cancellation as you move off axis. This is known as beaming and is usually controlled in speaker design by using drivers of the appropriate size for the frequencies they are reproducing. Changes in directivity with frequency are regarded as undesirable in speaker design, because although the on-axis measurements can be perfect, the ‘room sound’ (reverberation) has the ‘wrong’ frequency response.
A large panel speaker suffers from beaming in the extreme, but with Quad electrostatics Peter Walker introduced a clever trick, where phase is shifted selectively using concentric circular electrodes as you move outwards from the centre of the panel. At the listener’s position, this simulates the effect of a point source emanating from some distance behind the panel, increasing the size of the ‘sweet spot’ and effectively reducing the high frequency beaming.
There are other ways of harnessing the power of phase cancellation and summation. Dipole speakers’ lower frequencies cancel out at the sides (and top and bottom) as the antiphase rear pressure waves meet those from the front. This is supposed to be useful acoustically, cutting down on unwanted reflections from floor, walls and ceiling. A dipole speaker may be realised by mounting a single driver on a panel of wood with a hole in it, but it behaves effectively as two transducers, one of which is in anti-phase to the other. Some people say they prefer the sound of such speakers over conventional box speakers.
This all works well in terms of the direct sound reaching the listener and, as in the CBT speaker above, may provide a very uniform dispersion with frequency compared to conventional speakers. But beyond the measurements of the direct sound, does the reverberation sound quite ‘right’? What if the overall level of reverberation doesn’t approximate the ‘liveness’ of the room that the listeners notice as they talk or shuffle their feet? If the vertical reflections are reduced but not the horizontal, does this sound unnatural?
The interaction of a room and an acoustic source could be thought of as a collection of simultaneous equations – acoustics can be modelled and simulated for computer games, and it is possible for a computer to do the reverse and work out the size and shape of the room from the sound. If the acoustic source is, in fact, multiple sources separated by certain distances, the computer can work that out, too.
Does the human hearing system do something similar? I would say “probably”. A human can work quite a lot out about a room from just its sound – you would certainly know whether you were in an anechoic chamber, a normal room or a cathedral. Even in a strange environment, a human rarely mistakes the direction and distance from which sound is coming. Head movements may play a part.
And this is where listening to a ‘distributed speaker’ in a room becomes a bit strange.
Stereo speakers can be regarded as a ‘distributed speaker’ when playing a centrally-placed sound. This is unavoidable – if we are using stereo as our system. Beyond that, what is the effect of spreading each speaker itself out, or deliberately creating phased ‘beams’ of sound?
Even though the combination of direct sounds adds up to the familiar sound at the listener’s position as though emanating from its original source, there is information within the reflections that is telling the listener that the acoustic source is really a radically different shape. Reverberation levels and directions may be ‘asymmetric’ with the apparent direct sound.
In effect, the direct sound says we are listening to this:
but the reverberation says it is something different.
Might there be audible side effects from this? In the case of the dipole speaker, for example, the rear (antiphase) signal reflects off the back wall and some of it does make its way forwards to the listener. In my experience, this comes through as a certain ‘phasiness’ but it doesn’t seem to bother other people.
From a normal listening distance, most musical sources are small and appear close to being a ‘point source’. If we are going to add some more reverberation, should it not appear to be emanating as much as possible from a point source?
It is easy to say that reverberation is so complex that it is just a wash of ‘ambience’ and nothing more; all we need to do is give it the right ‘colour’ i.e. frequency response. And one of the reasons for using a ‘distributed speaker’ may be to reduce the amount of reverberation anyway. But I don’t think we should overdo it: we surely want to listen in real rooms because of the reverberation, not despite it. What is the most side effect-free way to introduce this reverberation?
Clearly, some rooms are not ideal and offer too much of the wrong sort of reverberation. Maybe a ‘distributed speaker’ offers a solution, but is it as good as a conventional speaker in a suitable room? And is it really necessary, anyway? I think some people may be misguidedly attempting to achieve ‘perfect’ measurements by, effectively, eliminating the room from the sound even though their room is perfectly fine. How many people are intrigued by the CBT speaker above simply because it offers ‘better’ conventional in-room measurements, regardless of whether it is necessary?
‘Distributed speakers’ that use large, or multiple, transducers may achieve what they set out to do superficially, but are they free of side-effects?
I don’t have scientific proof, but I remain convinced that the ‘Rolls Royce’ of listening remains ‘point source’ monopole speakers in a large, carpeted, furnished room with a high ceiling. Box speakers with multiple drivers of different sizes are small and can be regarded as being very close to a single transducer, but are not so omnidirectional that they create too much reverberation. The acoustic ‘throw’ they produce is fairly ‘natural’. In other words, for stereo perfection, I think there is still a good chance that the types of rooms and speakers people were listening to in the 1970s remain optimal.
[Last edited 17.30 BST 09/05/17]
Casual readers may not believe this, but in the world of audiophilia there are people who enjoy organising scientific listening tests – or more aptly ‘trials’. These involve assembling panels of human ‘subjects’ to listen to snippets of music played through different setups in double blind tests, pressing buttons or filling in forms to indicate audible differences and preferences. The motivation is often to use science to debunk the ideas of a rival group, who may be known as ‘subjectivists’ or ‘objectivists’, or to confirm the ideas of one’s own group.
There are many, many inherent reasons why such listening tests may not be valid e.g.
The tests are difficult and tedious for the participants, and no one who holds the opposing viewpoint will be convinced by the results. At a logical level, they are dubious. So why bother to do the tests? I think it is an ‘appeal to a higher authority’ to arbitrate an argument that cannot be solved any other way. ‘Science’ is that higher authority.
But let’s look at just the logic.
We are told that there are two basic types of listening test:
Presumably the idea is that (1) suggests whether two or more devices or processes are equivalent, or whether their insertion into the audio chain is audibly transparent. If a difference is identified, then (2) can make the information useful and tell us which permutation sounds best to a human. Perhaps there is a notion that in the best case scenario a £100 DAC is found to sound identical to a £100,000 DAC, or that if they do sound different, the £100 DAC is preferred by listeners. Or vice versa.
But would anything actually have been gained by a listening test over simple measurements? A DAC has a very specific, well-defined job to do – we are not talking about observing the natural world and trying to work out what is going on. With today’s technology, it is trivial to make a DAC that is accurate to very close objective tolerances for £100 – it is not necessary to listen to it to know whether it works.
For two DACs to actually sound different, they must be measurably quite far apart. At least one of them is not even close to being a DAC: it is, in fact, an effects box of some kind. And such are the fundamental uncertainties in all experiments involving the asking of humans how they feel, it is entirely possible that in a preference-based listening test, the listeners are found to prefer the sound of the effects box.
Or not. It depends on myriad unstable factors. An effects box that adds some harmonic distortion may make certain recordings sound ‘louder’ or ‘more exciting’ thus eliciting a preference for it today – with those specific recordings. But the experiment cannot show that the listeners wouldn’t be bored with the effect three hours, days or months down the line. Or that they wouldn’t hate it if it happened to be raining. Or if the walls were painted yellow, not blue. You get the idea: it is nothing but aesthetic judgement, the classic condition where science becomes pseudoscience no matter how ‘scientific’ the methodology.
The results may be fed into statistical formulae and the handle cranked, allowing the experimenter to declare “statistical significance”, but this is just the usual misunderstanding of statistics, which are only valid under very specific mathematical conditions. If your experiment is built on invalid assumptions, the statistics mean nothing.
If we think it is acceptable for a ‘DAC’ to impose its own “effects” on the sound, where do we stop? Home theatre amps often have buttons labelled ‘Super Stereo’ or ‘Concert Hall’. Before we go declaring that the £100,000 DAC’s ‘effect’ is worth the money, shouldn’t we also verify that our experiment doesn’t show that ‘Super Stereo’ is even better? Or that a £10 DAC off Amazon isn’t even better than that? This is the open-ended illogicality of preference-based listening tests.
If the device is supposed to be a “DAC”, it can do no more than meet the objective definition of a DAC to a tolerably close degree. How do we know what “tolerably close” is? Well, if we were to simulate the known, objective, measured error, and amplify it by a factor of a hundred, and still fail to be able to hear it at normal listening levels in a quiet room, I think we would have our answer. This is the one listening test that I think would be useful.
Last night I went to a symphony concert: Shostakovich’s 10th, preceded by Prokofiev’s Piano Concerto No. 2 at the West Road Concert Hall, Cambridge.
We were sitting in the second row from the front – so quite close to the piano. I wish I had taken a photograph, but I was so paranoid about my phone ringing mid performance that I left it turned off! The image above shows the empty venue.
We really enjoyed the concert. Chiyan Wong is an amazing piano soloist, and CCSO were spectacular. The sound was formidable from a large orchestra, and we got to hear the fairly new Steinway grand in great detail – the piano was removed during the interval, for the Shostakovich that followed.
Now, I do often listen to this sort of music with my system, but this was the first time I had been to a concert to hear this specific Russian ‘genre’. Of course I couldn’t help but make a mental comparison of the sound of the real thing versus the hi-fi facsimile that I am used to, as I was listening. And you know what? I have to say that a good hi-fi gives a pretty good rendition of the real sound.
The real thing was very loud, but also very rich – I have observed that ‘painfully loud’ is more a function of quality than volume; you need good bass to balance the rest of the spectrum. So this was very loud, but at no time painful. Bass from the orchestra was wonderful, but didn’t take me by surprise – I sometimes hear such bass from my system. (It did take me by surprise the first time I heard it from a hi-fi system, however!).
Some people cite piano as being the most difficult thing for a hi-fi system to reproduce. I don’t know where they get that from: I loved the sound of the piano, and I think a good system can reproduce it fairly easily.
I was struck by the homogeneity within the different sections of the orchestra. Listening to a recording of just a piano, or just the violins, would not tell you very much about an audio system. It is only when you hear a combination of the piano, the violins and the brass, say, that any ‘formant’ (i.e. fixed frequency response signature) within your system would show up.
As discussed previously, ‘imaging’ of the orchestra was not as pin sharp as you get in some recordings, but many purist recordings portray the true effect quite accurately. The width of the ‘soundstage’ of a stereo system is more-or-less right, and the room you are listening in enhances the recording’s ‘ambience’ around and behind you.
Of course the concert is a very special experience. The stereo version isn’t always as deep, open and spacious, nor is the envelopment as complete but, all in all, I think if you sit down in the right frame of mind to listen to a fine orchestral recording using a good hi-fi system, you are getting a very reasonable impression of the sound, excitement and visceral quality of the real thing. And that really is quite an amazing idea.
The short version…
The recent availability of DSP is leading some people to assume that speakers are, and have always been, ‘wrong’ unless EQ’ed to invert the room’s acoustics.
In fact, our audio ancestors didn’t get it wrong. Only a neutral speaker is ‘right’, and the acoustics of an average room are an enhancement to the sound. If we don’t like the sound of the room, we must change the room – not the sound from the speaker.
DSP gives us the tools to build a more neutral speaker than ever before.
There are endless discussions about room correction, and many different commercial products and methods. Some people seem to like certain results while others find them a little strange-sounding.
I am not actually sure what it is that people are trying to achieve. I can’t help but think that if someone feels the need for room correction, they have yet to hear a system that sounds so good that they wouldn’t dream of messing it up with another layer of their own ‘EQ’.
Another possibility is that they are making an unwarranted assumption based on the fact that there are large objective differences between the recorded waveform and what reaches the listener’s ears in a real room. That must mean that no matter how good it sounds, there’s an error. It could sound even better, right?
A reviewer of the Kii Three found that that particularly neutral speaker sounded perfect straight out of the box.
“…the traditional kind of subjective analysis we speaker reviewers default to — describing the tonal balance and making a judgement about the competence of a monitor’s basic frequency response — is somehow rendered a little pointless with the Kii Three. It sounds so transparent and creates such fundamentally believable audio that thoughts of ‘dull’ or ‘bright’ seem somehow superfluous.”
The Kii Three does, however, offer a number of preset “contour” EQ options. As I shall describe later, I think that a variation on this is all that is required to refine the sound of any well-designed neutral speaker in most rooms.
A distinction is often made between correction of the bass and higher frequencies. If the room is large, and furnished copiously, there may be no problem to solve in either case, and this is the ideal situation. But some bass manipulation may be needed in many rooms. At a minimum, the person with sealed woofers needs the roll-off at the bottom end to start at about the right frequency for the room. This, in itself, is a form of ‘room correction’.
The controversial aspect is the question of whether we need ‘correction’ higher up. Should it be applied routinely (some people think so), as sparingly as possible, or not at all? And if people do hear an improvement, is that because the system is inherently correcting less-than-ideal speakers rather than the room?
Here are some ways of looking at the issue.
The idea is also supported by some of the great and the good in audio.
“…we humans manage to compensate for many of the temporal and timbral variations contributed by rooms and hear “through” them to appreciate certain essential qualities of sound sources within these spaces.”
Or Meridian’s Bob Stuart:
“Our brains are able to separate direct sound from the reverberation…”
I think there is a formula that gives good results. It says:
Is there any scientific evidence for these assertions? No more nor less than any other ‘room correction’ technique – just logical deduction based on subjective experience. Really, it is just a case of thinking about what we hear as we move around and between rooms, compared to what the simple in-room FR measurements show. Why do real musicians not need ‘correction’ when they play in different venues? Do we really want ‘headphone sound’ when listening in rooms? (If so, just wear headphones or sit closer to smaller speakers).
This does not say that neutral drivers alone are sufficient to guarantee good sound – I have observed that this is not the case. A simple baffle step correction applied to frequency response (but leaving phase and timing intact) can greatly improve the sound of a real loudspeaker in a room without affecting how sharply-imaged and dynamic it sounds. I surmise that frequency response can be regarded as ‘colour’ (or “chrominance” in old school video speak), independent of the ‘detail’ (or “luminance”) of phase and timing. We can work towards a frequency response that compensates for the combination of room and speaker dispersion effects to give the right subjective ‘colour’ as long as we maintain accurate phase and timing of the direct sound.
We are not (necessarily) trying to flatten the in-room FR as measured at the listener’s position – the EQ we apply is very smooth and shallow – but the result will still be perceived as a flat FR. Many (most?) existing speakers inherently have this EQ built in whether their creators applied it deliberately, or via the ‘voicing’ they did when setting the speaker up for use in an average room.
In conclusion, the summary is this:
[Last updated 05/04/17]
Just saw this mentioned. It’s interesting how an idea that, years ago, was just a method of harnessing existing technology, can re-appear as something funky and brand new. It joins those other technologies that aim to get data into our devices via cost-free, non-contact interfaces, such as QR Codes.
What is Chirp?
A Chirp™ is a sonic barcode. With Chirp technology, data and content can be encoded into a unique audio stream. Any device with a speaker can transmit a chirp and most devices with a microphone can decode them.
People of a certain age will be familiar with the use of audio cassettes as storage for their microcomputer programs back in the 1980s – I think I used reel-to-reel for a time.
I also remember, round about 1980, sending a computer program over the phone to a friend’s house by holding the phone close to the speaker and picking the sound up at the other end with a microphone. As I recall, our version wasn’t really very reliable or practical, but I think we did succeed in sending a short program. Obviously we were inspired by the audio coupler modems that we might have seen in films and documentaries.
SMPTE and MIDI timecodes can be recorded as audio signals on analogue tape and can survive multiple transfers and, I dare say, would be robust enough to work over a speaker-microphone link.
In the 1990s we were all familiar with ‘the sound of data’ when we used dial-up modems.
Over the years we have also had DTMF dialling, audio watermarking, Shazam, Siri, Alexa etc. and phone-based automated systems using speech recognition, all of which have to deal with extracting ‘data’ from noisy audio. You would think that the new audio barcodes should be pretty simple to make work reliably.
Seen here. You could buy the mixing desk used for Dark Side of the Moon at auction this month.
UPDATE 28/03/17. It sold for $1.8m.
The 70s are back. Seen here, I very much like the look of this! I’ll bet the quality is probably rather better than the originals whose looks it is modelled on, too.
I would need three of them for my system, of course…
In The Secret Science of Pop, evolutionary biologist Professor Armand Leroi tells us that he sees pop music as a direct analogy for natural selection. And he salivates at the prospect of a huge, complete, historical data set that can be analysed in order to test his theories.
He starts off by bringing in experts in data analysis from some prestigious universities, and has them crunch the numbers on the past 50 years of chart music, analysing the audio data for numerous characteristics including “rhythmic intensity” and “agressiveness”. He plots a line on a giant computer monitor showing the rate of musical change based on an aggregate of these values. The line shows that the 60s were a time of revolution – although he claims that the Beatles were pretty average and “sat out” the revolution. Disco, and to a lesser extent punk, made the 70s a time of revolution but the 80s were not.
He is convinced that he is going to be able to use his findings to influence the production of new pop music. The results are not encouraging: no matter how he formulates his data he finds he cannot predict a song’s chart success with much better than random accuracy. The best correlation seems to be that a song’s closeness to a particular period’s “average” predicts high chart success. It is, he says, “statistically significant”.
Armed with this insight he takes on the role of producer and attempts to make a song (a ballad) being recorded at Trevor Horn’s studio as average as possible by, amongst other things, adjusting its tempo and adding some rap. It doesn’t really work, and when he measures the results with his computer, he finds that he has manoeuvred the song away from average with this manual intervention.
He then shifts his attention to trying to find the stars of tomorrow by picking out the most average song from 1200 tracks that have been sent into BBC Radio 1 Introducing. The computer picks out a particular band who seem to have a very danceable track, and in the world’s least scientific experiment ever, he demonstrates that a BBC Radio 1 producer thinks it’s OK, too.
His final conclusion: “We failed spectacularly this time, but I am sure the answer is somewhere in the data if we can just find it”.
My immediate thoughts on this programme:
-An entertaining, interesting programme.
-The rule still holds: science is not valid in the field of aesthetic judgement.
-If your system cannot predict the future stars of the past, it is very unlikely to be able to predict the stars of the future.
-The choice of which aspects of songs to measure is purely subjective, based on the scientist’s own assumptions about what humans like about music. The chances of the scientist not tweaking the algorithms in order to reflect their own intuitions are very remote. To claim that “The computer picked the song with no human intervention” is stretching it! (This applies to any ‘science’ whose main output is based on computer modelling).
-The lure of data is irresistible to scientists but, as anyone who has ever experimented with anything but the simplest, most controlled, pattern recognition will tell you, there is always too much, and at the same time never enough, training data. It slowly dawns on you that although theoretically there may be multidimensional functions that really could spot what you are looking for, you are never going to present the training data in such a way that you find a function with 100%, or at least ‘human’ levels of, reliability.
-Add to that the myriad paradoxes of human consciousness, and of humans modifying their tastes temporarily in response to novelty and fashion – even to the data itself (the charts) – and the reality is that it is a wild goose chase.
(very relevant to a post from a few months ago)
Have you ever suddenly been inspired to embark on a brand new hobby?
Maybe you’ve never owned a boat before, but having seen one chug by on the river you have thought “I’d love to do that!”. A quick browse in the classified ads shows lots of boats that look fine, and they don’t cost all that much. Basically any boat would be great, and you could gradually do it up, even if it is a bit shabby now. In your mind’s eye, your family will love you when you are able to take them on spur-of-the-moment, cheap weekends messing about on the water, starting in a few weeks’ time.
From this high point where the world is your oyster, you begin to take the advice of the magazines and other experienced hobbyists. Before you have even owned a boat, you become aware of the hierarchy of boat owners, and the boats that would render you a laughing stock if you owned them. You become aware of the general consensus on different types of bilge pump – not something you ever wanted to know. You begin to form an idea of the boat you should really go for – and it is not one of the bargain basement jobs you first saw. You might just about be able to stretch to a boat that would put you in the lower echelons of boat ownership but, importantly, not on the very lowest rung. You could always, perhaps, move up from there over time.
It now turns into an all-consuming hobby with the goal of having a boat on the river at the end of the year. In the end it costs thousands, and your children have grown up and left home before your boat finally takes to the water. You hit a bridge and rip the top off your boat the first time you take it out. You feel sick and abandon the whole hobby (a true story).
That’s the nature of male hobbies. They start out as wonderful, spontaneous ideas, but can turn into nightmares – mainly due to the existence of other hobbyists! Audio is one of those hobbies, I think. Ridiculously, the prices paid for bits of audio knickknackery rival the costs of boats.
A person could be seized one day by the idea of hi-fi as a way to improve their life, buy an amp and some secondhand speakers off Gumtree for £100, and plug their tablet or laptop headphone socket into the amp using a £2 cable. Hey presto, a hi-fi system that will sound much better than what they had before, and which has tinker-ability via the buying and selling of speakers and the audio streaming/library software options; there is no urgency in changing the amp and tablet hardware as they are pretty much perfect in what they do. The speakers are almost like pieces of furniture, so the person can indulge their tastes in how they look as well as how they sound, and they can be restored using standard DIY skills – a nice mini-hobby.
But what if the person does the natural male thing, and starts to read the magazines and forums? Immediately they will realise that their tablet’s headphone output is a joke in the audio world. They need to spend at least a few hundred pounds on a half-decent ‘DAC’, plus a couple of hundred on a budget cable. And of course, this is only for convenience: real audio quality can only be had if they own a decent turntable and a special vibration-free shelf to put it on. Where do they go from there? They need to make a decision on which turntable and which cartridge to go for. They need to take a view on cables, power conditioners, valve or solid state amps, accessories like cable lifters and record cleaning machines. Each decision, they are assured by their fellow hobbyists, will result in “night and day” differences in the sound.
After some months agonising over it, they assemble a beginner’s system for about £3,000 – they will upgrade as budget allows. It sounds OK, but they know that even though the brand is a highly recommended one, the particular model of valve amplifier they could afford has “hints of a slightly reticent mid range” – one of the magazines said so – and if they listen carefully, perhaps they can hear that… But the more powerful 18 Watt model cost £800 more and they decided against it. Perhaps they made the wrong decision. The nightmare unfolds…