The Digital Lens

August 12, 2015
 by Paul McGowan

I have been involved with many successful designs of audio accessories, but two stand out: the HCPS and Digital Lens. The first came about by accident, the second by design. Today we focus on the second.

I have likely written on the subject of the Lens before but it seems worthy to do it again in different words. The Digital Lens is a regenerator for digital audio. LIke the venerable Power Plant AC regenerator, a Lens recognizes incoming data, throws away the original, rebuilds new and jitter free digital audio before the DAC gets it.

First produced in the mid 1990's, the product was a wild hair idea of mine designed, developed, prototyped and crafted by our Chief Engineer, Bob Stadtherr. Final tweaking and voicing was performed by my partner in Genesis Technologies, Arnie Nudell. We had noticed the output of DACs varied greatly with different cables and transports. Neither Arnie nor I bought into the 'bits is bits' foolishness, but frankly we were surprised at the extent they mattered. We both suspected timing and wave shape as culprits.

Most engineers rely on postulates to visualize the mechanisms of problems. If timing (jitter) were to blame for variations in sound quality, I had imagined we could prove that by removing the suspected clock/data relationship. We know jitter does not occur in stored data without reference to a clock. It is only when that data and clock are paired we risk jitter. Therefore, multiple copies of identical data, even those delivered over disparate mechanisms, should sound identical when output from a storage device controlled by a common clock.  Thus, the audio RAM buffer was 'invented' to solve sonic differences.

RAM buffers were not new, though their use in an accessory to improve DAC performance was. We soon learned there was much more going on that also needed fixing and we'll cover that list tomorrow.

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13 comments on “The Digital Lens”

  1. Are there plans for a regen type product from you ?
    I have three of them now.
    They are much cheaper now the last one was about 300 with a linear psu
    It's use almost as good as a server built for purpose.
    Lastly do you plan to make a server perhaps a combo pwt / network and usb server. That would be a great product of needed combination
    My msb UMT plus is such a device and does a great job.
    Sorry if this was not the intention of this post if I am wrong.
    Al

  2. Hello Paul!
    I'm really not happy on your saying ' ‘bits is bits’ foolishness.
    In bits '1001' equals '1001'!
    Only if one has real difficulties with eyesight one could read 'f00l'.
    I hope mixing up things that shouldn't be mixed up will belong to the past.
    BTW I might be wrong, but if I remember well it was Wadia with their 2000 DAC, who were first talking about jitter in digital audio.
    Greetings

    1. Sorry, don't mean to make anyone unhappy, but bits ain't bits when it comes to getting them into an audio reproduction device sounding the same.

      You are absolutely correct that 1001 is the same as 1001 - but the timing of when those two bits arrive and the shape they're in, how they affect the power supply and a hundred other variables affect everything around those bits and change the sound.

      So, I don't mean to be so quick to say things like that, most readers of this blog know what I am referring to and I apologize for any misunderstandings.

      1. OK Paul!
        That is another cup of tea, because it relies to the electrical signal.
        To draw a comparison approach, One can read black letters very well if they were printed on white paper, it is more difficult to read them on dark grey paper and nearly impossible if they were printed on black paper. Nevertheless one has printed the same information 😉
        Greetings

        1. agreed, and thus my statement 'bits aren't bits' until they get into the device in proper order and form. There were many myths perpetrated on us that neither cables nor recording medium mattered where bits are concerned - bits are bits - and how you present them, whether on black paper the machine cannot read, or white paper it can, doesn't matter.

          We know better.

  3. Here is test data from Stereophile Magazine for the Genesis Digital Lens. Is this the same product you are talking about Paul?

    http://www.stereophile.com/content/genesis-technologies-digital-lens-measurements#WKClFeW3tPQMiPIJ.97

    Looking at the data, IMO the results are inconclusive and irrelevant. To begin with testing at -90db is absurd. That does not emulate real world conditions. Secondly, some of the data seems to show what I'd consider marginal improvement, other data shows degradation. Again the test conditions are IMO absurd. If this is what it takes to demonstrate any differences between this product and other products or no product, then I find it unconvincing.

    I haven't had time to read the entire article yet. I'm not sure how this is any different from merely using a Schmidt Trigger to resquare the waveform from hf (rise time) degradation due to shunt capacitance and series inductance and reclocking using an SSR with a highly stable clock. As I understand it a RAM is just an SSR connected head to tail with variable input and output points. Jitter induced by interconnect wires can be sharply reduced by simply locating the D/A converter directly adjacent to the CD transport optical to electrical read electronics on the same circuit board. Much of the problem if it really is a problem seems to be created by the interconnect wires themselves. High end products that create problems more high end problems have to be used to solve???

    From Wikipedia; A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. While there are several differing types, it is easy to initially visualize as an electronic circuit consisting of a variable frequency oscillator and a phase detector. The oscillator generates a periodic signal. The phase detector compares the phase of that signal with the phase of the input periodic signal and adjusts the oscillator to keep the phases matched. "Bringing the output signal back toward the input signal for comparison is called a feedback loop since the output is 'fed back' toward the input forming a loop."

    "Keeping the input and output phase in lock step also implies keeping the input and output frequencies the same. Consequently, in addition to synchronizing signals, a phase-locked loop can track an input frequency, or it can generate a frequency that is a multiple of the input frequency. These properties are used for computer clock synchronization, demodulation, and frequency synthesis."

    I saw my first phase locked loop around 1970 built from discrete components. It was quite a project built as part of a complex electronic measuring instrument by GE I was evaluating for Bethlehem Steel. Not long afterwards PLLs became available at low cost in IC versions. It's actually old technology but still very useful for many applications. The PLLs I've seen use input tracking filters to keep spurious noise from knocking the circuit out of synch lock. It therefore can be considered an integrator. The VCO output can be converted to whatever you want it to be for external use such as a square wave, sine wave, triangle wave, pulse etc. From there it has to go to the D/A converter, one more opportunity to create jitter in the connecting wires.

    1. It is very different than a simple trigger.

      First the incoming data are multiplexed together with an embedded clock in what's known as S/PDIF. What normally happens is the multiplexed data is separated into its components parts: data and multiple clocks. The clocks are then used to drive the D/A converter.

      The first two issues you run into is the method used to recover the clock creates jitter. The second problem you run into is the clock was generated by a CD transport in the first place, and that clock is usually jittered - depending on the CD player - but rarely any good.

      What the Lens did is unraveled the multiplexed data, threw away all clock information and placed the data itself into a RAM buffer. The size of the buffer varied with the speed of incoming data (for obvious reasons). Once full we then used an excellent low jitter clock that was fixed - clocks inside CD players are variable and change according to the speed of data recovered from the laser - to reassemble (multiplex) the data back into S/PDIF and on its way again.

      1. Yes, the RAM is the reclocking mechanism. It's like the second amusement park ride I explained below. It is clear that reclocking must happen in the transport because the disc itself can never spin at nearly the stability and accuracy of speed required for digital audio.

  4. A lot of people here like analogies so I’ve thought one up to explain jittering and dejittering as I understand it. Consider two amusement park rides one in front of another. In each ride there is a long train of cars one seat wide. If a seat is occupied it’s a one. If it’s empty it’s a zero. The train advances one seat at a time. When the seat arrives at an exit gate in ride one, the gate opens and if there is someone in the seat they get out. If it’s empty, nothing happens and after an interval the gate closes. The train of cars advances to the next seat and the cycle repeats. When the passengers get out of ride one, they walk to the entry gate of ride two where they get on. If there is someone at the gate when it opens, they get in. If no one gets in during the fixed interval the gate closes anyway and advances to the next car. The object is to have filled and empty seats in the same order, that is the same configuration in ride two as it was in ride one. Problem, they don’t all walk from ride one to ride two at the same speed. That’s the jitter. If they arrive at ride two within the interval allowed while the gate is open for the correct seat in the sequence, it doesn’t matter. The rate at which gate two opens and closes controls whether or not they’ll get into the correct seat. Ride two reclocks them.

    What happens if the passenger arrives too early or two late for the seat he’s supposed to be in on ride two? Then the sequence of ones and zeros is wrong and the D/A converter will program the wrong voltage for the analog signal. In the analog domain this will show up as distortion or noise. So you can relate the analog performance to the jitter inherent in the digital domain and whether or not it is beyond the tolerance of what the reclocking circuit can handle before it is converted back to analog form. Measured distortion even for inexpensive CD players is invariably very low. Is digital jitter really a problem? I’m not sure but so far I’m not convinced. Will fancy dejittering equipment make an audible difference? Probably yes but that doesn't prove the change is the result of dejittering. There are other variables in play too. To prove dejittering matters, all of the other variables must be eliminated or taken into account. Is different the same as better? I dunno???? Maybe, and then again maybe not. 🙂

  5. Hi..

    I have a few questions regarding the Digital Lens technology. Excuse me for being a decade too late but I own a PWD + Bridge I and im quite exited. I stream the music from Tidal and from my NAS. The sound is far greater than anything I've ever owned and im head over heels. As I've understood it the Bridge is capable of re-clock the signal. The nativeX mode in the dac also re-clocks the signal. Is there any significance re-clocking twice? - or am I completely off?

    Best,
    Young but dedicated (and ten years behind) hifi geek, Michael

    1. The reclocking Lens in the Bridge is separate from the input of the PWD but they are not related. So if you're using USB or another source to the PWD it goes through the input Lens. The streaming option of the Bridge has a separate Lens different from the input Lens.

  6. I've been playing a lot of live Blu-Ray concerts at 48kHz/24Bit (as I found out painfully, BluRay AVHCD does not support 96kHz/24Bit via S/PDIF) but does via HDMI (WTF ?)

    I've been switching to the 2.0 tracks on live concert BluRay's and DVD's using the PCM S/PDIF input of the SGCD/Preamp lately. I'd never done that on previous AVR's I've had in the past. The Digital Lens concept works. Stop "thinking" about and trust your ears, man !

    Again Cheers to the Weekend !

    Joe

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