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HIFICRITIC 2008 October News.
Regular visitors to the site will notice many changes, some still underway.
We have added a HIFICRITIC FORUMS covering music and stereo equipment matters and we are already impressed by the quality of both our participants and their responses, pretty thoughtful stuff.
The Sound Quality Archives will be updated. Many more back reviews will be uploaded, available free of charge. Currently, we are working on a HIFICRITIC Authors section, inevitably partly dependant on author contributions, so you can find out more about the team.
Paul Messenger and I wrote a series of technology guides some years ago and we now have permission to reproduce them. Look out for the recent Technologies Explained (A12-A14) uploads in our Archive Pages.
Many thanks to all subscribers and those who have re-subscribed. New subscribers are key to the development of the project so please everyone else know what you think of us and encourage them to join us.
HIFICRITIC attended the Manchester Audio Show at the airport Radisson SAS 26th to 27 Jan 2008. (See the Manchester show blog ). We met many of our readers, signed up newcomers and fielded numerous technical and system queries. Please let us know what you would like to see covered in future in the journal.
A month later we arrived at Bristol for the Sound and Vision Show, (See the Bristol show blog ) Friday 23rd to Sunday 25th Feb at the 'Mariott City Centre Hotel'. Our reception was as brilliant as last year and we welcomed all our friends with a good turnout of HIFICRITIC authors, including the Editor, Paul Messenger. Now in our second year we find that we are gaining increasing respect and acceptance from the audio industry. We put out a Bristol show blog and there were a number of interesting technology and product introductions at this show.
HIFICRITIC also attended the Munich HIGH END Show, HIGH END® 2008 and while we did not exhibit we presented a paper for the lecture series on the performance of Class D amplification entitled: ARE CLASS D AMPLIFIERS HIGH FIDELITY? We also reported on interesting aspects of this important European audio show.
We have just tidied up after the September 2008 Heathrow Show and Paul Messenger has posted his show report above. (See Manchester show blog)
Issue11 is completed which was mailed out in September 2008 and which has some fascinating content. Issue 12 is in preparation and includes a big survey of loudspeaker and interconnect cables. See ‘Upcoming’.
In writing up the cartridge reviews for Issue 7 (Vol2 No 1) model were so helpful that we have obtained permission to reproduce the general text on our site, and many thanks to Symmetry and Sumiko for helping make this happen. Download Sumiko Cartridge setup instructions here.
British High End Audio Manufacturer enters the Phone Business
Chord Electronics enters the phone business with their new product launch at the Sheraton Park Lane Hotel. Two products were showcased, not prototypes, rather full working models, with pre production already under way and retail orders in hand , including Sevenoaks Sound and Vision.
While the project was reaching maturity earlier in the year it was too soon to publicly release it at the Munich Show, and while I knew of it, I could not discuss it until this London release.
How do you associate high quality audio with a mobile telephone?
Buried in the Bluetooth wireless transmission standard is an uncorrupted coded audio signal, digital and full resolution, like S/PDIF, and present on nearly all modern handsets. It is called A2DP and no one has ever thought to use it. Using it is not as simple as that, and Chord conducted significant research into the subject in cooperation with the Finnish engineers involved in founding Bluetooth, resulting in a unique decoding chip in order to achieve mute free reliable transmission at the highest quality. At present there is audio over Bluetooth but it is not so reliable and is decoded to a barely average quality level, intended mainly for hands free headsets.
Having looked at the extant iPod market and the concept of these larger stores of audio that need to be accessed by a physical or wired connection and are generally loaded up via a computer and matching software, Chord have decided to jump forwards.
Chord is gambling on the increasing penetration of often short term downloaded music to mobile phones. The rapid growth in large inexpensive memory for phones is fuelling this development. Once there, it is wholly logical for the younger market to bypass conventional systems, even stationary music and net servers, and wish to play at high quality at home, straight from the phone.
QBD76 semi transparent view
QBD76 showing rear panel interfaces
Proof of concept is an audiophile 'digital to audio' product called the QBD76 which is itself a massive working of their well regarded DAC 64 for hi fi systems, and costs a substantial £3,000. I heard this 24 bit resolution device through a £30,000 audio system and it sounded just fine, top CD quality in fact, but then founder John Franks revealed that what I was hearing was transmitted from the Sony-Ericsson mobile in his pocket, with uncompressed, full resolution WAV files. I asked about transmission stability and in response he chucked the phone to an assistant at the back of the hall who proceeded to juggle with it and two others while proceeding out into the hotel beyond. The result; uninterrupted, high dynamic range audio. 20m transmitting range is solid, 30m is usually attained.
Then a much smaller unit was revealed, still finished in Chord's trademark super fine, burnished, anodised aluminium. Merely 'very good' rather than full-on audiophile, this does the Bluetooth digital audio capture and replay too, at a fraction under £400 and should still be genuine hi fi.
Franks has dubbed this one the 'Chordette Gem'
Chordette Gem Bluetooth Digital audio player with aerial
The Chordette Gem colour range
www.chordelectronics.co.uk
Copyright HIFICRITIC 2008
23rd UK AES conference 9,10 April 2008:
'Music Everywhere'
New Hall College, Cambridge
Blog by Martin Colloms.
HIFICRITIC 2008
Many thanks to all subscribers who have already re-subscribed, and there is still time to take advantage of the discount offer for those who haven't yet. Due to great demand it has been extended to March 31st 2008. New subscribers are key to the development of the project so please everyone else know what you think of us and encourage them to join us.
HIFICRITIC attended the Manchester Audio Show at the airport Radisson SAS 26th to 27 Jan 2008. (See the Manchester show blog ). We met many of our readers, signed up newcomers and fielded numerous technical and system queries. Please let us know what you would like to see covered in future in the journal.
A month later we arrived at Bristol for the Sound and Vision Show, (See the Bristol show blog ) Friday 23rd to Sunday 25th Feb at the 'Mariott City Centre Hotel'. Our reception was as brilliant as last year and we welcomed all our friends with a good turnout of HIFICRITIC authors, including the Editor, Paul Messenger. Now in our second year we find that we are gaining increasing respect and acceptance from the audio industry. We hope to put out a Bristol show blog quite soon and there were a number of interesting technology and product introductions at this show.
We have just completed Issue 8 which is scheduled for mail out in very early March 2008 and which has some fascinating content. Responding to requests we have reviewed a batch of five integrated amplifiers from £500 to £800. One was capable of 250W per channel four ohm loading for music programme, was inexpensive and sounded good! Most were UK designed while one from Japan had UK design support in the form of custom 'voicing' from UK's Air Studios. This issue also assesses two high performance wall mount speakers, one on-wall of improbably slim and self effacing profile, and one which is improbably expensive and is optimised for near wall location. Both may help solve conflicts arising for free space location and room interior design.
HIFICRITIC is attending the Munich HIGH END Show, HIGH END® 2008 and while not exhibiting we will present a paper for the lecture series on the performance of Class D amplification entitled: 'ARE CLASS D AMPLIFIERS HIGH FIDELITY? We will also report on interesting aspects of this important European audio show.
In writing up the cartridges for Issue 7 we found that the Sumiko setting up instructions for their Blackbird moving coil were so helpful that we have obtained permission to reproduce the general text on our site; many thanks to Symmetry and Sumiko for making this happen. Download Sumiko Cartridge setup instructions here.
HIFICRITIC Class D Switching Amplifier Debate
Our Issue 5 evaluation (Sept/Oct) of four recent and highly significant Class D amplifiers has raised something of a controversy and we are now subject to heated discussion on the audio forums including Pinkfish.
We began this evaluation with an open mind and took scrupulous care in trying to answer the many questions raised about sound quality and to subsequently seek useful information which might help to explain the results.
All models were well run in. They were auditioned prior to the lab testing, so that the listening findings would not be prejudiced by prior knowledge of the test results.
None of the amplifiers did well in the auditioning. All showed numerous artefacts in lab testing which past experience has shown may have been responsible, at least in part, for some of the observed variations in sound quality.
While we hoped that these recent examples would begin to justify the voluminous hype seen in the media over their claimed value and performance, particularly sound quality, we could not verify the reports and claims which been made.
Two kinds of audio listener?
However the project did raise an important issue concerning how audiophiles and audio designers perceive sound, how they interpret music, and what qualities they value in both live musical performance and in sound reproduction.
Without wishing to appear excessively judgmental, the sound quality results from our team, when compared with the much more positive results reported by some other listeners seem to suggest fundamental differences in perception.
According to the first kind of listener: "I can hear clear sounds, the bass is powerful, solo instrument focus is highly defined. It drives my difficult speakers well, and, this amplifier is cool, clever, compact, convenient, ecological and good value."
Conversely, the second kind says: "I want to tap my feet, I want to hear the life, expression and natural dynamics which help make it sound more like real music. I want the image to be stable, with deep three-dimensional perspectives; I want sparkling high resolution treble sounds which image in depth. I want a natural timbre and tonal balance."
From personal experience I know that to be a member of the second group you need to have had experience, ideally on good quality familiar recordings, of how well these qualities can in fact be expressed in a well tuned and matched audio replay system.
Those who have not experienced these music performance qualities from reproduced audio may never know or understand what is possible. They probably run a system which has not been selected to reveal these qualities, and are therefore unlikely to be able to detect whether they are present or absent in any other component introduced into the system. The system becomes a self sustaining closed loop encompassing the listener.
It's important that the audio system in which a product is evaluated has the potential to reveal most of the important parameters, both those helpful to listener involvement and those responsible for detail, bandwidth, power and spatial effects. Only then will the musical performance differences which we consider so important be sufficiently revealed.
It seems that the first listener group are more accepting of the balance of performance provided by Class D amplifiers, whereas those in the second group may appreciate certain aspects of Class D performance, but viewed as a whole find them dissatisfying at present.
We hope to explore this listener divide in future issues of HIFICRITIC.
Technical comment:
Some of the technical reasons why this might be so are explained in that fifteen page Class D feature, issue 5, covering ProJect, Bel Canto, NuForce and Channel Islands Class D amplifiers, and including comment on earlier Yamaha, Sharp, Sony and Flying Mole designs.
Briefly summarising the test findings, 'switching amplifier', Class D designers seem to be perfectly happy to discard several decades of audio engineering wisdom which have helped shape the creation of many great sounding pure analogue products.
From a technical viewpoint it now seems permissible to:
- Feed broad-band radio frequency noise into the power supply outlets
- Feed broad-band radio frequency noise to the line and ground connections
- Drive broad-band radio frequency noise into the speaker cables and loudspeaker. (up to 500MHz with up to 2V generally measured at around 50kHz)
- Define the output impedance using a significant passive filter, with a result which varies with frequency and is dependant on speaker loading
- Allow the amplifier to be marginally or completely unstable with either high or open circuit output loading
- Employ soft compressor clipping circuits prior to full power clipping to prevent feedback saturation.
- Employ high order negative feedback to improve in-band distortion figures and low frequency output impedance.
- Specify numerically high damping factor at low frequencies and claim that this guarantees fine bass.(regardless of the interface to the loudspeaker or any other property of the circuit)
- Use steep low pass filters to limit the upper high frequency range, partially negating the purpose of wider bandwidth, source material e.g. SACD, while the resulting filter phase shifts may be audible in the working band.
- Have low bandwidth input circuits which are highly susceptible to stray high frequency input signals, including upper band noise shaper signals and DAC artefacts. The result is poorer treble sound quality and measurable distortion.
- Have power output circuits with poor high frequency resolution resulting in high levels of intermodulation products at the high frequency end of the spectrum
- Have 'sampler' noise-shaped noise floors. The latter vary dynamically with the level, frequency and complexity of the input signals.
- Have comparatively small power supply reservoirs, in the light of their low frequency output current potential and available power.
- Have thermal dissipation limitations due to the small power module size which means that dynamic variations are present in the performance with time and temperature.
- To protect the fragile output stages all kinds of pre-clip and aggressive fold back protection regimes are included which are frequency dependant and are also programmed for duty cycle. Unexpected sound quality variations may result when operated at higher powers and with more difficult loads.
- Operate at an equivalent sample rate which is insufficient for good resolution above 7kHz. DSD, 1 bit pulse-width modulation operates at 2.4MHz, nearly ten times the usual rate presently used in Class D amplifiers.
- Deliver high, constant DC voltages (up to 70V) relative to local ground at the output terminals and hence also the loudspeaker connections and cable. (not of course between the +,- terminals as both of these are at the same dc potential)
- Use a high feedback switch mode power supply which has to react dynamically to the power draw variations of the power amplifier with the music programme. Generally these are designed for supplying dc and are demonstrably imperfect faced with near audio bandwidth loading at a wide dynamic range. Essentially the supply constitutes a form of audio amplifier yet it was never intended to be optimised for such duty.
Comment:
For a linear amplifier designer the presence of even one or two of the above eighteen listed integers would generally be regarded as potentially prejudicial to sound quality of the design.
From this viewpoint the odds seem to be stacked against the switching amplifier as applicable to high quality audio applications.
Perhaps instead of criticising, we should instead be applauding the Class D designers for achieving what they have in fact achieved against all the odds!
HIFICRITIC 2008
