Saturday, 20 March 2021

A look IN the Audio Precision APx555 B-Series. Thoughts on price and value in audio products.

From our "RETRO-MEASURE" of a 1980's cassette tape player a couple weeks back, let's make a 180° turn, look at some photos, and chat about "state of the art" performance gear this week!

A reader awhile back had the need to do some hardware work on the Audio Precision APx555 B-Series machine and in the process, was able to take a few photos of the innards, sharing it with me. The B-Series audio analyzer is the latest and greatest audio measurement device from AP. It was announced in December 2018 and here's a nice review from 2019 in audioXpress.

I thank my friend for sharing the images and helping me to understand some of what I'm looking at here. :-) There are no schematics publicly available of course so my comments will be in broad strokes and I'll leave it to the engineers reading this to examine deeper - click on the images for a higher resolution view.

I don't think I've ever seen pictures of the inside of these AP machines online but obviously the Internet is a big place so perhaps I have missed them. There is actually a good reason why you're not likely to see the insides of something like the APx555 - it's a calibrated device. It costs US$30,000+ to buy one of these. You'll be breaking 2 seals if you crack it open, that will also break calibration confirmation, and voids warranty the moment it's tampered with.

I have been told that the calibration is complex, resulting in a 4-page set of readings across all kinds of signals and analyses. It's an expensive and time-intensive process with custom software and precise external instruments to get the job done. Few companies are allowed to do this and typically the machine will need to be shipped back to AP.

At this price point and with the technical know-how that's needed to get the job done, I don't think it's a stretch to say that small boutique audiophile manufacturers likely do not have access to one of these to use in their research and development.

The picture above was taken with the cover off looking from the rear of the machine. At the top of that image is the front panel where all the input/output connectors are located and you will find different options installed. Here's a front panel image from the AP website:

As you can see, the machine is modular and arranged in 2 "compartments", a top portion and a bottom portion. The top part is where the analogue stuff plugs in, the bottom portion typically for various additional digital modules like the "Advanced Digital I/O", "PDM", "Digital Serial I/O" (eg. I2S) and Bluetooth (SBC, AAC, full aptX codecs supported). They also have a HDMI+ARC module.

For completeness, here's the back panel:

This device needs to be connected to a computer through the USB Type B 2.0/3.0 interface (ASIO driver supported) where tests are run using the AP software. This makes the system very flexible in that the software can be updated easily and likewise you can upgrade the computer, monitor, etc. over time. The APx555 also has firmware upgradability.

The XLR and BNC connectors (bottom right) are the Advanced Master Clock module. The RS-232 ports are for auxiliary in/out controls and one labelled "Software Options" for the AP KeyBox dongle to run certain software versions.

If you want to be impressed by a thorough user's manual, you can register and download the manual here. It's a 750+ page document with not only instructions on the myriad uses of this product (including speaker acoustic measurements) but contains interesting tidbits on measurement standards and the meaning of some of these tests (Chapter 80 p. 525 onward particularly relevant). Page 735 is a great description of units of measurement and we see from p. 741 on an excellent glossary of terms/acronyms with concise definitions. Excellent resource even for hobbyists like myself!

Let's have a closer look inside and behind that front panel:

We can see a nice separation of the analogue input and output sections. Each section separated to left and right channels with replication of the circuitry. The board looks very clean. "Everything in its place, a place for everything" as one would expect for a state-of-the-art device. As a reminder, we're looking at just the top compartment with its multiple circuit board layers here.

If we look at the portion on the right, here's a closer examination of the analogue output section. This section includes the Analog High Performance Sine Generator, capable of 5Hz to 204.457kHz output with superior signal purity than the digital generator. There's analogue square wave generation (<2μs rise time) and low-distortion sine burst as well supported:

The vertical boards appear to be power stages with transistors on them. Unbalanced output can go up to 13.3Vrms, double that to 26.7Vrms balanced.

The upper-level board to the right might be the signal generator portion itself with trim pots for calibration. There's a DAC function that allows the playback of arbitrary signals (0.001Hz-80.1kHz according to the literature). Interestingly, the device also allows simultaneous DAC and analogue generator to feed different signals to the analogue outputs (p. 43 manual).

And to the left of the signal generator / analogue output in the labelled image above, we see the analogue input portion which contains the ADC chips:

A close-up of the front portion of this board:

For each channel we have a pair of ADCs: AKM AK5394A, and Analog Devices AD7760. The AK5394A is a delta-sigma device that can operate up to 192kHz without a rising noise floor above 20kHz (great for measurements). Compared to others, this is a relatively expensive ADC and power-hungry (I've read that it may require up to 1W). The AK5394A has been discontinued for awhile now so presumably AP bought up a bunch of these for their devices.

The AD7760 is a higher speed part that can perform conversion up to the 1MHz that the AP supports. Note that there is a resolution difference between the two chips so precision is highest up to 96kHz bandwidth (192kHz) and drops beyond that which is fine since we're talking about ultra-ultrasonic frequencies!

We can see a few relays probably for changing the impedance and the input board also has an "autoranging" feature for various input levels. Maximum voltage input of 160Vrms unbalanced, and 300Vrms balanced split across 11 ranges!

The APx555 incorporates a precise analogue notch filter for each input. This >100dB (!) filter removes the fundamental ("1st harmonic") leaving the residual signal to analyze with a specification of -120dB THD+N "typically". Presumably the large Xilinx and Cyclone FPGAs are part of the magic performing the analogue/digital signal integration and bandpass filtering. As per AP block diagram in Technical Note 124:

To the rear of the machine, we see what looks like a "computer" portion.

There's a SODIMM DDR3-1866 RAM stick (probably 4GB if it's a dual-sided board). There's maybe a low-power CPU under the heatsink. Some FPGAs seen. Presumably all of this is to handle communications primarily through the USB-B port (the rectangular connector in middle-top of the picture). The machine runs its own OS, one could guess it's some type of Linux variant and likely explains the size of the firmware updates. A fan to keep the section cool.

Just beside that computer/USB communications portion is where the power supply sits. The power supply is a custom unit, but looks similar to what one might find in a computer. Note there's another fan behind the power supply (removed in image):

Since moderate noise isn't a problem in a lab environment, these machines can be unpleasant if one is working from a quiet home environment I am told. I guess best to not have them running in your soundroom. :-) 

Here's the front section of the analogue signal generator section where we see relays galore! A number of them would be used to change output impedance for the generator for balanced and unbalanced output (40-600Ω range, mute, feature to run balanced XLR with only +/- connected and so on). We see some transistors on the vertical boards to drive the analogue outs.

My friend took a picture just underneath the signal generator board also:

Another Altera/Intel Cyclone V FPGA. Not sure what this is for. The use of all these FPGAs means a significant level of programmability and upgradability.

Looking at the lower compartment, here's the "Advanced Digital I/O" module that comes standard. You can see the circuitry for S/PDIF/AES. Trimmer pots for precise calibration of parameters like AES level, rise time and even optical TX jitter:

There's a metal plate that shields this underlayer from the top analogue in/out compartment. Optional boards are installed in the space over to the left of this image.

Looking at these pictures, this is obviously a "high tech" product filled with plenty of advanced know-how. Just look at the sheer number of parts needed to put this thing together and what would have clearly amounted to years of team efforts in research and development! Although we're just looking at the hardware here, let's not forget the years of software/firmware/FPGA development as well. The quality is described as top notch with really no professional competition in sight. ~US$30,000 is certainly not an astronomical price for a state-of-the-art machine like this. In fact, my friend tells me it's "worth every penny" for precise audio design work. He has in fact found that AP's published specs for this machine are at times conservative for the performance it's actually capable of.

Perhaps like me, while reading and looking at these innards, you might also be thinking about the high-priced audiophile products in magazines or see at the local dealers. These days, asking price for many audiophile products easily compete with the AP's "mere" $30,000. If we look inside audiophile "high end" electronics that cost $30,000, would we see similar levels of technology and would we admire the sheer amount of work needed to produce such a machine?

Looking around audiophile sites, we have source electronics like the Lampizator Pacific DAC "demanding" this kind of price - have a look at the circuit board here. Old-skool products like the Audio Note UK Jinro integrated amp for example also "demands" this kind of cash, check out the picture of the innards in Stereophile; is there enough in there to be worth $30G even with a very healthy markup?

Without even discussing the most expensive products in their lineup, how about these Nordost Odin Supreme Reference Power Cords for a mere US$16,800/2.5m. An absolute steal at half the price of one of these APx555B machines! (Maybe AP should consider these cables for even better performance? ;-)

HiFi Inside (ex-HiFi Shock) has a large collection of naked audio hardware pictures as well if you're into these kinds of photos BTW.

I know, tube DACs, amps, cables, AP audio analyzers serve different purposes so it's comparing "apples and oranges". Nonetheless, like many "high end" devices, the AP is a rather niche product as well and I'm sure they don't make too many every year such that you can say the company is able to lower the price per unit due to economy of scale. As tech products developed through engineering, I think there's something to be said about the intellectual ability and creativity required when we consider the intrinsic value of the electronics.

I hope this has been fun "audiophile geek porn" for the more-objective "hard core"!


To end, I think this post gives us an opportunity to consider the idea of value in the technological products we buy.

As in all financial transactions, whether it's paying the guy mowing your lawn or buying investments, we are inevitably faced with finding the balance between "price" and "value". As Warren Buffett said: "Price is what you pay, value is what you get". Both will vary over time, although price tends to be the one that fluctuates more. Sentiment and demand are the foundations for supporting an actual transaction price; just because something is advertised at an MSRP means little unless a transaction has actually happened and settled at that number.

I think for most of us here, thinking about price isn't as interesting as considering the value of something. While there are different ways to think about this, it's probably useful to break the concept up into subtypes: absolute value, relative value, and perceived value.
Absolute value refers to the intrinsic abilities, unique features, workmanship/labour costs, and material costs of the product.
Relative value is determined by looking around at competitors and trying to uncover relative abilities/characteristics of a product within the arena of others. 
Perceived value is determined by the buyer him/herself and "Gotta have it!" emotional sentiments. The need for gratification of that desire drives demand.
For an expensive purchase, decision-making is typically complex, and we integrate all 3 definitions of "value". As a "more objective" audiophile, I typically tend to lean towards examining the "absolute value" of a device first. Product specifications, features, objective measurements and tests give me an idea about the intrinsic abilities of the product which I can then judge using the concept of high fidelity as the goal because sound quality is the "prime objective" in audiophilia, right? However, as human, I certainly will not deny myself the pleasures of owning something "cool" if that's what I desire (high perceived value) and of course I still would like to get a good deal in the process (good relative value compared to other similar devices by other companies).

Notice that the priorities I list above are somewhat different to the goals in advertising or if I may be blunt, much of the subjective reviews I read/watch online or in print media surrounding new products. Typically, the advertiser's goal is to increase if not blatantly hype up the perceived value primarily. Techniques like celebrity endorsements can be a very powerful tool to enhance the perception. I suppose in a way "big name" senior reviewers and prominent audio magazines have a psychological effect like those celebrity endorsements as well. As sophisticated consumers, I trust we're all well aware of this dynamic.

Inevitably, I believe the more dubious a product - like expensive cables, unorthodox room tweaks, bit-perfect luxury computer streamers - the more the company must bolster perceived value since there are no actual gains to be had by spending more money.

I see that these days, many subjective reviewers have become a bit more cautious about their claims (good that they're recognizing the limitations of their own hearing/memory/abilities). At times we see attempts to compare products, but usually this is in the domain of "look and feel", material workmanship (which of course will affect price) or other subjective characteristics rather than through claimed reliable comments about sonic quality. Frequently we end up with summary statements like this about sound quality:
"For absolute hi-fi sounding resolution, I would go with SuperDuper's Amp One. However, if I wanted a luscious soundstage and great spatial depth, I preferred UltraPrime Amp A!"
Such a statement would provide quotable endorsements for both manufacturers and neither SuperDuper nor UltraPrime should be offended. The Golden Ear reviewer retains his air of connoisseurship, and everybody's happy right? But has the consumer truly learned anything?

Since I have no interest in purchasing an APx555B as a hobbyist, personally the "demand" is low. However, I can still appreciate the absolute value of what has been accomplished and the results this machine produces. The years of R&D invested by the company has yielded a product that is able to perform in unique ways. If I were an audio engineer aiming to make a high performance product, there is no question that a $30,000 investment would likely bring me great rewards. As long as there is a need to design these high performance audio products, there will be a demand for the AP box.

On the other extreme are those expensive audiophile products I listed above. For some, an Audio Note tube amp, Lampizator tube DAC, and the Nordost Odin power cable are presumably of high perceived value such that they are worth the asking price. However, I think many of us would question the absolute value of these products or their relative value compared to competitors. In fact, one might even argue with good confidence that much less expensive products could perform just as well if not better for high fidelity audio reproduction. The uniqueness of these products is not necessarily with what they can do (certainly not with that power cable IMO!), but what emotions some attach to them. The moment emotional sentiment is undermined, so too demand and whatever perceived value.


Well friends, it's Spring Break time! I hope you're all enjoying some good weather... Even though I'm not going anywhere special this year, it's still good to catch some R&R.

Hope you're all enjoying the music!


  1. But how does it sound connected to a hi-fi system? That is the question. :D

    1. Hey Matias,
      Good question, I'll have to ask my friend how the DAC signal generator sounds :-). I assume one could perhaps do a loopback measurement to see what kind of resolution he gets...

      Even a simple 1kHz THD+N from the digital generation might be interesting!

  2. Where's a picture of the power cable the AP comes with? ;)

  3. Price should reflect the aggregate subjective value judgements of the consumers. For some aggregation of consumers the $16,000 power cable reflects their collective subjective value. Perhaps that cohort of consumers would assess the value differently with more perfect information and perhaps not. Sites like this one help to balance against the marketing megaphone.

    It will be interesting to see how things develop in the home audio market. My personal value judgements have certainly been modified and my listening enjoyment improved through applying information from objective sources and experimenting with gear that measures well. It's nice to have confidence in the gear and enjoy the music.

    1. Hi Doug,
      Yup, ultimately the value equation will be an aggregate and there's no underestimating the subjective contributions!!!

      The marketing megaphone is massive and ultimately it's up to each of us audiophiles to seek out opinions in the face of this bias. The nice thing is that the Internet has all kinds of information now available for free and I hope to be doing my part in this time of the history of the audiophile hobby...

      Keep up the experimentation, Doug!!!

  4. Can Audio Precision APx555 B-Series work as a DAC? I would be interested to know how it sounds.

    1. Hi fgk,
      I don't have access to the device but my belief is yes... The digital signal generator should be able to play whatever signal you wish to play.

  5. How timely; I've been wondering a lot about this myself. The cost to manufacture/price ratio seems particularly low with cables. What specifically does it cost Audio Quest to make those multi-kilobuck cables? This seems completely inexplicable when you compare that to the cost to manufacture their cheapest cables, which seem equally well-made. It's almost as if there is an agreed-upon silence on the subject of cost to manufacture versus price that seems to be something like "I won't bring it up if you don't" - dare I say it - conspiracy of sorts among expensive cable makers...
    And this problem is exacerbated when you have "very high costs is invariably directly proportional to listening pleasure" reviewers like Michael Fremer, who has never heard an uber-expensive product the didn't love. (Fremer in particular seems almost to flaunt those ridiculously high prices even though he couldn't possibly afford them himself).

    Ther are a few reviewers who seem to avoid taking the asking price charged versus the cost to build annd simply avoid products that are ridiculously expensive to the point where they're not worth the stratosferic price charged - Kalman Rubinson, Herb Reichert and the late Art Dudley come to mind ) - but most so -called "high-end" reviewers are like Fremer: "This one costs more than that one so it de facto is better." That fact alone makes their recommendations essentially math-driven and often sycophantic. Yet anyone can simply figure out relative prices for themselves.
    Tom Sylvester

    1. Hi Tom,
      Yup, well put. I don't think it would be at all paranoid to say that there is a tendency for an industry based on hype and false claims to "keep mum" about that which IMO they all know about. The job is to maintain confidence (hence the "con" game) in their claims to keep the "cohort of consumers" (in the words of Doug above) happy and hooked on the supposed value of these products.

      Those multi-kilobuck cables are all nonsense IMO. A scientifically minded consumer could just as well say the same about other "industries" humans put value in in this world - paranormal healers, homeopathy, astrologists, fad diets, feng shui, all kinds if faith-based organizations, etc. So it has been for thousands of years and I'm sure thousands more.

      Whatever we can do in this little hobby to improve rationality and hopefully in the process rewarding the companies that actually do something to improve sound quality would be good... As opposed to scam companies that take money from "the faithful".

      As for Fremer. That kind of simplistic hyping based on relative price is rather sickening. It really calls into question the motivations and "vision" these kinds of writers have when it comes to high-fidelity audio. I want to see the day when every person is able to enjoy excellent performance at reasonable prices. I believe we're there already in many digital products like DACs. There needs not be "classes" of products when it comes to sound quality because technology has reached a point where reproduction has universally approached if not exceeded the threshold of human acuity in the hardware. When that time comes, all that really matter is how well artists and production folks can create their vision. Again, I think we're there in many respects since "mastering" is often the limiting factor to sound quality already!

      People like Fremer can still tout and patronize their preferred companies but it will be because of "class", not sound quality. Just like an expensive LV handbag might be desired by some over a Coach, it would not be because anyone claims that the LV bag can perform its utilitarian function (ie. carrying your credit cards and cash) any better than the cheaper bag.

      A website like this interviewing Fremer is an example of an obvious attempt at putting the "class" structure into audiophilia:

    2. Thanks much for the thoughts, Archimago. And for the link to the Mono and Stereo Review article. (That blog itself is a paean to the "it costs so much that it must sound really terrific" philosophy.) There Fremer says "anyone who doesn't think AC cables make a difference simply hasn't bothered listening." How is that any different from someone saying "reviewers that claim to hear things that are 'beyond measurement' are simply liars shilling for the cable industry"?

      But Fremer is grossly, notoriously egotistical, so let's not demolish his professed world view anymore lest we become cliched ourselves.

      In his excellent book "Fundamentals" Frank Wilcsek says this: "...extrasensory perception, telekinesis, prayer-induced miracles and magical thinking assign prominent roles in shaping the course of physical events to mind and will. Most of those ideas are [seen by their proponents as] "reasonable" extensions of the world-models we build up as children, in which our mind is disembodied and our will controls our body."

      Others of us grow up and become adults.

  6. Archimago,

    I struggle with the idea of value in audio all the time.

    One one hand:

    The prices for some high end gear just seems prima facie absurd. Especially the cable racket, where the prices almost seem like a dare. It feels like if there is any objective fact about value in this cold universe, it is that many high end cables are vastly overpriced and the result of the most amazingly cynical dare for anyone to pay the price.

    And the prices seem to have a trickle-down effect of raising prices generally.

    Further, the idea that "something is worth whatever someone pays for it" seems to have an uncomfortable nihilism. I mean, do we just completely abandon any notion of a "rip-off?" Of "being taken for a ride" or "scammed?" Does it say nothing at all about the person who puts together a piece of well-performing gear, pairing down price as much as he can given his costs, vs the person who throws together the same gear but puts a massive sticker price on it "because he'll find someone who will pay that much?" Is there no comment in there about what type of motivations or people we are looking at?

    On the other hand:

    How would a more objective scale of value justify many of the things I own?

    I have plenty of items in the high priced bracket, which could be outperformed likely at less cost. But they are "valuable to me" which seems to throw things right back in to the subjective.

    Wrangling through these issues on my own, think about things this way. Taking an example of a product that I really love and would like to own: the Devore Fidelity O/96 speakers.

    These are one of those speakers that have been decried by the "measurements crowd" and even some of the DIYers because "you can get much 'better' - accurate - measuring speakers for far less." And "it's just a two-way in a big box, gussied up with a nice finish to hike the price way up for the suckers."

    (BTW, certainly not everyone is that cynical about them, and there are arguments for why those assessments are maybe facile...but going with it).

    So why would I want to spend a whole bunch of money on a pair?

    My personal answer is: I auditioned a large number of speakers, everything from great-measuring Revels, Magicos, and also many like Paradigm, Focal, tons of others, and the particular character of the Devores utterly grabbed me in a way the others didn't. I wanted to sit and listen far more than the other ones I auditioned.

    But does that make the big cost "worth it?"

    Well...yeah. What are the alternatives for me? I could get in to DIY and build some lower-cost version...but I don't want to make speaker building a hobby (time, money, lack of interest). It's like going to a fine restaurant and someone saying "you could learn to make this at home, you know, with lots of training!" Well, yeah, I don't want to, which is why I'm paying someone else to do it.

    My view is that even IF it were true that the price is high for what one is getting, the fact is THAT is the sound that turns my crank and I'm not able to find it for the same price or cheaper elsewhere. So if I want THAT sound then that's the money I have to pay. Is it worth it to me therefore? Yes, just as it would be worth it if I had found the Revel or other speakers were the one that grabbed me. (And, again, the idea the Devore price is somehow cynical I think is naive, in terms of the realities of running a speaker company).

    So that's one way I work through the idea of value. Of course there are all sorts of other considerations. I use CJ tube amps, far more expensive than any number of SS amps that would be more accurate and cheaper to buy and own. But I can't find the sound they give me in those cheaper amps, even if it's a coloration I like. And there are added things I value like the looks, build quality, the conceptual/aesthetics of what tube amps look like and how they work, the history, etc.

    1. Hi Vaal,
      Yeah, the phenomenon is interesting when it comes to the fracturing of prices in the audio world. As you noted, there are "classes" of products like cables that are climbing like NFTs and cryptocurrency :-). But at the same time, we have "down to Earth" companies like Schiit, Topping, SMSL, etc. that are making some genuinely good stuff IMO at least the equivalent of these luxury-audio brands (let's not even call them "hi-fi" because many are not or even "hi-end" but what they really are).

      I appreciate your struggle when you said "Further, the idea that "something is worth whatever someone pays for it" seems to have an uncomfortable nihilism."

      I agree, in a world where anything someone believes in goes, I still hold on to the old fashioned idea that it is morally incorrect for a person or company to scam people with fraudulent claims. I believe that history has always gone in cycles and for those of us young enough to live through the next few decades, I think we'll see a time of "regression to the mean". Just look around at the main writers for magazines like Stereophile, their time as mouthpieces for the industry are clearly in the final inning.

      Certainly when it comes to personal preference like not being able to get the same sound out of other speakers compared to the O/96 then absolutely, pay what you have to; it's your money! I'd still look for a good deal or used of course but I don't think you're being scammed in any way since the design characteristics clearly result in a type of sound. Zu speakers are another one that I know some people love even though I was thoroughly unimpressed at RMAF 2019 at their display. These are small companies with limited supply so the law of supply and demand is strong.

      This is different from things that truly make no difference (like kilobuck power cables vs. any decent gauge IEC). Sure, an objectivist who holds on to the Harman research of Spinorama data and measurements like the "directivity index" might be unimpressed by the Devore, but we must always remember that the research is based on "averages". Just because the data says that "on average", listeners preferred this or that kind of sound, does not mean you or I must agree. At best, predictive value of some of these models are around 85% anyways - not bad but more than 1 in 10 will disagree.

      A scientist must respect the idiosyncrasies of being human. But at the same time be able to call BS on the scams.

    2. Regarding your statement that so-called "professional" reviewers "time as mouthpieces for the industry are clearly in the final inning": their sickening embrace of MQA as "obviously superior to anyone wqho listens instead of measures"(including Hartley's tediously unschooled blathering about "post-Shannon sampling") have really helped grease the skids under those clowns. I still read some of them (Greene, Atkinson and Rubinson to name a few) but most of the rest are dispensable.

  7. I was able to rent an Audio Precision unit for my needs, while doing research and development into my DAC. Much less expensive than purchasing a unit, and it came calibrated. I did later purchase a Prism Sound dScope Series III and used that for a while.