Publisher Profile

An Interview with Alan Langford of DEQX

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Laurence Borden: Alan, welcome to dagogo. Please begin by telling us about your background, including of course electronics and audio.

Alan Langford: My interest in audio started when I was around 10 years old when some friends and I started removing parts from old televisions and radios and discarded equipment to make our own amplifiers & speakers. While studying electronic at university back in the 1980s, I started working at a high-end audio retail store in Sydney. I owned all manner of equipment and wasn’t tied in to one particular technology. I owned electrostatics and dynamic speakers, valve and solid-state amplifiers, you name it.

DEQX HDP programming bench

LB: When did DEQX begin, and what is your role in the company?

AL: DEQX formally began in 2001 and was co-founded by Kim Ryrie. Kim Ryrie was also the co-founder of the globally successful Fairlight Instruments who produced the first digital sampling computer musical instrument (CMI). The Fairlight system was used by such artists as Peter Gabriel, Stevie Wonder and various others, and had a marked impression on musical production in general in the 1980s. The team at DEQX has many years of experience in advanced digital design. I joined DEQX in 2008 and the first project was the HDP-3. My role is as DEQX’s General Manager. In conjunction with Kim Ryrie, I am also involved in the hardware design of our products.

LB: Let’s turn now to the DEQX products. Your products serve various functions, which we’ll discuss individually, with the understanding that the whole is more than the sum of its parts. Let’s begin with the crossover function. All DEQX models have at least two outputs — high and low — for integration of main speakers with a subwoofer, while the more expensive models have high, middle, and low outputs, and are thus capable of serving as an active cross-over for a typical three-way speaker. Please explain the benefits — and drawbacks, if any — of an active crossover, as compared to the much more commonly used passive crossovers. As part and parcel of that question, why are active crossovers so uncommon in high-end audio?

AL: The ‘Mate’ series of products are designed to allow integration of passive loudspeakers with one or more active subwoofers. The products enable the user to linearize both the frequency and phase domains, thus providing seamless addition between the main speakers and subwoofer(s).

Our HDP series offers fully active linear phase 3-way crossovers. This allows the consumer to change a passive loudspeaker to active, or to build his or her own active speaker configuration.

Passive crossovers must be designed to handle whatever power the amplifier delivers but they’re inefficient because of component losses; this is especially true of the more complex crossovers. They also disrupt phase accuracy (linear-phase) when the crossover slope is greater than 1st order. They are widely used because they’re cost-effective to build, and provide a ready to go solution.

Active speakers use separate amplifiers for each bass, mid and tweeter driver but the amplifiers only have to supply the frequency requirements of each respective drive unit. Also, by the amplifier’s output stage being directly connected to each driver, the damping factor control is much improved.

We feel there are only advantages to using an active crossover versus a passive one. The only drawback to an external active crossover is system complexity in terms of multiple amplification devices and their associated costs. Unlike a conventional passive speaker, the tweeters and midrange drivers do not require high power and costly amplifiers due to spreading the speaker load across multiple amplifiers. For example, a 10-Watt amplifier would be sufficient for a tweeter and a 50-Watt amplifier will suffice for a midrange driver.

Deqx-HDP4-speaker-rear

LB: Active crossing over can be done in the analogue or digital domain; why did DEQX choose the latter?

AL: The issue with analogue crossovers, either passive or active, is that they can’t compensate for phase errors at the crossover point. Digital crossovers are at least minimum phase and allow for higher crossover slopes with minimal phase anomalies. DEQX is unique in that we use linear phase processing (FIR filters) and crossovers, which completely eliminate phase errors.

LB: Now let’s turn to a second function, that of room correction. Why do you think room correction has such a bad reputation amongst high-end audiophiles?

AL: While the DEQX’s primary function is not room correction, I’m unsure about the accuracy of the term “bad reputation.” Maybe it’s a case of a lack of products addressing room correction at the high-end market. In other words, I suspect that most high-end audio users may not have experienced the potential benefits of a well-engineered speaker and room correction product.

LB: The DEQX literature suggests two ways in which your approach differs from that of your competitors; the first difference is that you correct the speaker first, then the room, rather than correcting “just” the room. The second difference is the claim to correct not just the frequency, but also the phase. How are these implemented, and why are they beneficial?

AL: The DEQX processor first calibrates the speaker’s frequency response/time domain (impulse response correction). We’re making the speaker anechoically flat as far as both frequency response and group delay.

How it works

Equalization (EQ) is regarded suspiciously in audiophile circles. And rightly so. In trying to correct the tonal balance caused by the significant frequency-response errors endemic to loudspeakers, timing (phase) delays are introduced to varying degrees for some frequencies.

Loudspeaker phase delays (timing errors) are about 100 times worse than are present in the signal driving them. Although the delays are consistent for every speaker design (be they electromagnetic type, planar, ribbon or electrostatic), correcting them has been impossible in the analogue world. Expensive engineering is usually required to minimize phase delays but even these design compromises can have undesirable effects. For example, traditional shallow crossover filters can maintain linear phase but can’t properly quarantine drivers to their ‘linear’ operating zone. This results in reduced dynamic resolution (compression) and less natural dispersion due to driver on-axis ‘beaming.’

DEQX, however, corrects existing phase delays already introduced by the loudspeaker.

The first graph (frequency response) is a low distortion speaker driver’s frequency response. This response falls within the mandatory plus/minus 3dB zone required through the mid-range frequencies for even average ‘hi-fi’ speakers.

After DEQX correction (the blue line) its frequency response has become truly accurate.

The second graph (group-delay response) shows how the speaker delays some frequencies to varying degrees. Notice that some frequency groups lag by around one millisecond (1ms), others are not so delayed and still others are even more so. After DEQX correction, all of the audio has been delayed by approximately 10ms to allow the late frequencies to catch up (the upper curve) when the signal is reassembled.

The speaker’s frequency-response and timing coherence have been restored to more precisely reflect the audio signal.

frequency

LB: All DEQX models have volume controls; is this mediated in the digital domain? If so, how is it implemented so as to prevent throwing away necessary bits?

AL: Correct. As you point out, to avoid discarding “necessary bits” the DEQX volume is processed at full 32-bit floating point within the DSPs and not within the fixed environment of the DACs. At any reasonable listening level 24-bit resolution is maintained.

LB: The presence of a volume control allows DEQX units to be connected directly to an amplifier(s); i.e., without the use of a preamplifier. Like so many things in audio, this too is controversial. On one side of the debate are those who feel that the fewer components there are in the signal chain; the better; on the other side are those who maintain that systems without active preamps suffer a loss of dynamics. This leads to a few questions: First, can DEQX systems be configured with a preamp? (I assume the preamp would have to be upstream of the DEQX, so as to control all channels.) If so, the second question is, which configuration do you prefer (recognizing that this may be system-dependent). And last, what can you tell us about your analogue stage, which in the absence of a preamp, communicates directly with the amplifiers?

AL: Yes, any DEQX processor can be used with a preamplifier. Many hours of R&D have been put into the ADC to maintain transparency and to maintain the sonic character of upstream components. Any changes in cables, preamps, etc. will be reflected in the sound produced; the DEQX does not exert its own character on downstream components. The implementation of DEQX is system-dependent and we don’t have a specific preference in terms of how it is used; we just demand that it does not impinge upon the downstream components’ sound. The DEQX is in effect a preamplifier. Its analogue output stage is in common with many high quality preamplifiers.

LB: Do DEQX products allow for multiple inputs, for example, a computer/music server, an optical transport, and perhaps a phonostage?

AL: Our preamplifiers, PreMate, Express 2 and HDP-4 have two analogue inputs, four digital (Optical, two S/PDIF and AES/EBU). All models can accept the XMOS-based 24/192 USB audio option.

LB: High end audio is undergoing a major shift, with the closing of “Brick and Mortar” retailers, and increasing reliance on direct sales. How has this impacted the DEQX business strategy? As part and parcel of that question, what type of customer support do you offer, especially with regard to the complexities of room correction?

AL: I would say that while there is a shift away from retailers for low to mid-fi products, high-end audio products are still the domain of the bricks and mortar retailer. In some cases a bricks and mortar retailer today may trade from a residence rather than a shop front but still provide the level of service required for this market.

As DEQX requires some degree of knowledge and experience to obtain the best results, we still recommend and support bricks and mortar dealers where they are able to provide installation and product support. DEQX also offers a remote set-up service, called the DEQXpert, for those wishing to set-up themselves or for customers in remote locations.

LB: Alan, thank you for taking the time to speak with us. Perhaps you could leave us with some final thoughts as to what you see for the future in terms of digital correction.

AL: I see this concept expanding in the low to mid-fi markets at a steadily increasing rate with less complex and budget solutions. In the high-end it will be a more bespoke solution provided at the speaker manufacturing level where solutions may be targeted at singular products and situations.

I appreciate your providing this opportunity to talk about the DEQX products, of which we are quite proud. I hope your readers found it informative, and will consider the benefits that a DEQX product can bring to their audio system

http://www.deqx.com/

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