Category Archives: hifi

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Devialet’s Phantom audio system on show in Barcelona

I was glad to see and hear the French Devialet Phantom system at the Mobile Focus event in Barcelona, just before Mobile World Congress, having missed the company’s recent presentation in London.

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The Phantom is a device that looks like a giant eyeball, and is essentially an active mono wireless DAC and speaker. There are two models, the Phantom which delivers up to 99dB at 1 metre and costs €1690, and the Silver Phantom which delivers up to 105 dB at 1 metre and costs €1990. There is an optional Dialog unit at €299 which is a wi-fi router that creates a private network for the Phantom as well as supporting a guest network designed for music sharing. A Dialog can also control up to 24 Phantoms and is necessary for multi-channel; obviously for stereo you need at least two. An app called Spark runs on iOS, Android or Windows (not Windows Phone) and handles playlists as well as visualising music.

Each Phantom has a midrange unit, a treble unit, and two woofers. It measures 253 x 255 x 343mm and weighs 11 kg.

My encounter with Phantom did not get off to a good start. I am allergic to misleading jargon, and the pitch the Davialet representative made to me was confusing to say the least. “Digital chops up the sound,” he told me; but with hybrid technology Devialet was able to reproduce the purity of analogue sound. I observed that every DAC in the world is able to decode digital formats to analogue sound, and we had some difficulty progressing to what exactly is different about Devialet’s approach.

The case for the Phantom is not helped by the over-the-top language in the brochure, which modestly claims “the best sound in the world” and under a heading “IN TECHNICAL TERMS” promises Zero distortion, Zero background noise and Zero  impedance.

The system was playing Hotel California by the Eagles when I was there. I know the sound of this album well and it sounded boomy and unpleasant, though it is difficult to get good sound on a stand in a busy exhibition so I make generous allowance for that.

I did get a copy of a white paper which offers a bit more information. There are several technologies involved.

The first is what Devialet called ADH (Analog/Digital Hybrid). This combines class A amplification with the efficiency of class D. The way Devialet puts it is that several class D amplifiers act as slaves to the class A amplifier, so that the class D amplifiers provide the power while the class A amplifer the control.

A Texas Instruments PCM179x DAC is positioned next to the amplifier to minimise any loss between the two.

Next comes SAM (Speaker Active Matching) which processes the audio to compensate for the characteristics of the drive units. This “takes place ahead of the DAC and power amplifier section” according to the paper, so you could think of it as a kind of digital pre-amplifier. SAM has “a mathematical model of the complete drive unit, accounting for the electrical, mechanical and acoustical behaviour.”

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A third feature has the name HBI (Heart Bass Implosion). This tackles the tricky problem of reproducing deep bass with a small enclosure. The idea is to use a sealed box design for high efficiency at the lowest frequencies, a driver with long 26mm excursion (the difference between the foremost and backmost position of the driver) in order to move more air, and to use two symmetric drivers to cancel mechanical vibrations.

This does result in high maximum air pressure inside the enclosure, up to 174dB SPL according to Devialet’s paper. Most drivers collapsed in this environment, so Devialiet designed its own woofer.

Finally Devialet’s engineers figured that a sphere is the ideal shape for producing sound without “diffraction loss”.

The result, according to the specs, is 16Hz to 25kHz +- 2dB, and 20Hz to 20kHz +- 0.5dB which is impressive for a speaker system.

The problem with such measurements is that they typically taken in an anechoic chamber whereas actual listening rooms have all sorts of resonances that result in a much less accurate sound.

Does Devialet’s Phantom system sound as good as a more traditional system at its price level? That is the question which interests me; if I get an opportunity to try it out I will be sure to report back.

Playing native DSD with Raspberry Pi 2 and Volumio

There are many intriguing debates within the world of audio, and one which has long interested me concerns DSD (Direct Stream Digital). This is an alternative technology for converting and recovering sound from digital storage. The more common PCM (Pulse Code Modulation) works by sampling sound at very short intervals and recording its volume. By contrast DSD records the difference between one sample and the next, sampling at an even greater frequency to compensate for the fact that it only captures a single bit of data in each sample (ie on or off). For example the standard used by CD is:

16-bit precision, 44.1 kHz sampling rate

and by SACD (a DSD format):

1-bit precision, 2.8224 MHz sampling rate

The SACD was introduced by Philips and Sony in 1999 as an upgrade to CD, since it is a higher resolution format cable of a dynamic range of 120 dB and frequency response up to 100 kHz. It was an effort, like the PCM-based DVD Audio, to convince the public that the CD is not good enough for the best quality sound.

SACD was largely unsuccessful, mainly because there was not really any dissatisfaction with CD quality among the general public, and even some experts argue that CD quality already exceeds what is required to be good enough for human hearing.

That said, SACD was popular in the niche audiophile community , more so than DVD Audio. Some listeners feel that SACD and DSD results in a more natural sound, and believe that PCM has some inherent harshness, even at higher-than-CD resolution. Enthusiasts say that DSD stands for “Doesn’t sound digital”. For this reason, there is a regular stream of new SACD releases even today, and DSD downloads are also available from sites like Native DSD Music and Blue Coast Records. Some DSD downloads are at higher resolution than SACD – Double-rate or Quad-Rate.

The resurgence of DSD has been accompanied by increasing availability of DSD DACs (Digital to Analogue Converters). While these tend to be more expensive than PCM-only DACs, prices have come down and a quick eBay search will find one from under £100.

There are several complications in the DSD vs PCM debate. While DSD is a reasonable format for storing digital audio, it is poor for processing audio, so many SACDs or DSD downloads have been converted to and from PCM at some point in their production history. If PCM really introduces harshness, it is presumably too late by the time it gets to DSD. That said, it is possible to find some examples that are captured straight to DSD; this can work well for live recording.

Another complication is that some consumer audio equipment converts DSD to PCM internally, to enable features like bass management.

Is there any value in pure DSD? I wanted to try it, preferably with DSD files rather than simply with SACD, since this is much easier for experimenting with different formats and conversions as well as enabling Double DSD and higher. Unfortunately SACD is rather hard to rip, though there is a way if you have the right early model of Sony PlayStation 3.

The first step was to get a DSD-capable DAC. I picked the Teac 301 which is a high quality design at a reasonable price. But how to get DSD to the DAC? Most DSD DACs support a feature called DSD over PCM (DoP), which conveys the DSD signal in a PCM-format wrapper. DoP is not a conversion to and from PCM, it merely looks like PCM for better compatibility with existing playback software.

Next, I used a Raspberry Pi 2 supplied by Element14 (cost around £25.00) and installed Volumio, a pre-built version of Linux which includes an audio streamer and web-based user interface. You download Volumio as a single file which you burn onto a micro SD card using a utility such as Win32DiskImager. Then you plug the card into the Pi, connect to a home network via Ethernet and to a DAC via USB, and power on.

After a minute or two I could connect to Volumio using a web browser.

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My music is stored mostly in FLAC format but with a few DSD files in Sony’s DSF (Digital Storage Facility) format, and located on a Synology NAS (Network Attached Storage). In Volumio’s menu I went to Library and mounted the network share containing the media. Next, I tried to play some music. PCM worked, but not DSD. I changed the playback settings to enable DoP:

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Success: My DSD files play perfectly:

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If you squint at this image you will see that the 5.6 MHz light is illuminated, indicating that the DAC is processing Double DSD.

It sounds lovely, but is it any better than the more convenient PCM format? I am sceptical, but intend to try some experiments, using a forthcoming audio show to find some willing listeners.

That aside, I am impressed with the capability of the Raspberry Pi for enabling a simple and cost-effective means of playing DSD over the network, although with the assistance of an external DAC. It plays PCM formats too of course, and with Volumio is easily controlled using a mobile device, thanks to the touch-friendly web UI.

Fun with amplifiers: classic Naim versus modern Yamaha integrated

Every year in an English country hotel near Melton Mowbray a strange but endearing event takes place.

Called variously the HiFi Wigwam Show (after the forum that runs it) or the Scalford HiFi Show (after the hotel where it takes place), this is a show where most of the exhibitors are enthusiasts rather than dealers, and the kit on show includes much that is old, unavailable or home-made – like these stacked Quad 57s from the Sixties.

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I turned up at Scalford with a simple experiment in mind. Take a classic pre-power amplifier from thirty years ago and compare it to a modern, budget, integrated amplifier. What kind of differences will be heard?

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The classic amplifier is a Naim 32.5 preamp powered by a Hi-Cap power supply, and a 250 power amplifier. Price back in 1984 in the region of £3500. The Naim was serviced around five years ago to replace old or failing electrolytic and tantalum capacitors.

The integrated is a Yamaha AS500 80w+80w amplifier currently on sale for around £230.

The source is a Logitech Media Server (Squeezebox Server) with a Squeezebox Touch modified to work with high resolution audio up to 24/192, and a Teac UD-H01 DAC. Speakers were Quad 11L, occasionally substituted with Linn Kans for a traditional Linn/Naim combination. A BK Electronics sub-woofer was on at a low level to supplement the bass.

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A QED MA19 switchbox was used to switch instantly between the two amplifiers. Naim NAC A4 cable was used throughout.

Disclaimer: this was not intended as a scientific investigation. Level matching was done by ear, and there were several aspects of the setup that were sub-optimal. The system was in a small hotel bedroom (as you can see by the headrest which forms the backdrop to the system) and thrown together quickly.

Still, the Naim amplifier is both highly regarded by many audiophiles, and also considered somewhat coloured, this failing more than mitigated by its pace and drive. The Yamaha won awards as a good budget amplifier but is not really anything special; however it has the benefit of modern electronics. These two amplifiers are very different both in age and (you would think) character.

A benefit of the setup was that both amplifiers were always on. Unless you knew the position of the switches and how they were wired, you could not tell which was playing. It was irresistible; when visitors asked which was playing I switched between them and said, you tell me.

Again, this was not science, and I have no tally of the results. Some visitors confidently identified the Naim and were correct, and an approximately equal number were incorrect. Some said they simply could not hear a difference, and two or three times I had to prove that the switchbox was working by twiddling the controls. A small boy who probably had the best hearing of all the visitors declared that there was no difference.

Note that I did reveal the identity of the amplifiers at regular intervals, so listeners typically listened sighted after listening blind.

Of those who expressed a preference, the Yamaha and Naim were each preferred equally often. Some said the Yamaha was slightly brighter (I agree with this).

There were two or three who expressed a strong preference for the Naim, but the consensus view was that the amplifiers sounded more alike than had been expected.

The sound was also pretty good. “I would be happy with either” was a common remark. I would have preferred to use high-end speakers, but the Quads proved delightfully transparent. Most visitors who heard both preferred the Quads to the Kans, which sounded thin and boxy in comparison, though I do wonder if after thirty years the crossover electronics in the Kans may need attention. It was easy to hear the difference between high quality and low quality sources. I used some of the high-resolution files which Linn kindly gave away as samples for Christmas 2013, along with other material.

A few reactions:

Tony L: The most amusing room for me was the Naim 32.5 / HiCap / 250 blind-test vs. the Yamaha AS500. That was great fun, and yes, I picked the AS500 as better. Twice. As did another ex-32.5/Hicap/250 owning friend. Ok it was through a nice easy to drive pair of Quad 11Ls, but you’d be amazed by how close they sounded!

YNWOAN: I heard the Yamaha/Naim demo and had no difficulty hearing a difference between the two with the Yamaha sounding rather ‘thin’ – even at the low levels used.

Pete the Feet: How cruel can a man be? Pitching a recently serviced Naim 32.5, Hicap and NAP250 against a paltry Yamaha £250 integrated. Not much difference but the Yamaha had the edge.

Some felt that the Naim was compromised by the stacking of the power supply and pre-amp on the power amp. There was no hum and I am sceptical of the difference moving them apart, or using acoustic tables, might have made; but of course it is possible. Another interesting thing to test would be the impact of the switchbox itself, though again I would be surprised if this is significant.

How much should you spend on an amplifier? Should all competent amplifiers sound the same? These are questions that interest me. I set up this experiment with no particular expectations, but the experience does make me wonder whether we worry too much about amplification, given that other parts of the audio chain introduce far more distortion (particularly transducers: microphones and loudspeakers).

A more rigorous experiment than mine came to similar conclusions:

How can it be possible that a basic system with such a price difference against the  reference” one, poorly placed, using the cheapest signal cables found, couldn’t be distinguished from the more expensive one?

And, most of it all, how come the cheap system was chosen by so many people as the best sounding of the two?

Shouldn’t the differences be so evident that it’d be a child’s game to pick the best?

Well, we think that each can reach to its own conclusion…

One further comment though. I love that Naim amplifier, and do not personally find something like the AS500 a satisfactory replacement, despite the convenience of a remote control. Is it just that the classic retro looks, high quality workmanship and solid construction convince my brain into hearing more convincing music reproduction, provided I know that it is playing? Or are there audio subtleties that cannot easily be recognised by quick switching?

Unfortunately the audio industry has such fear of blind testing that these questions are not investigated as often or as thoroughly as some of us would like.