RETRO-MEASURE: 1994 Sony MDP-750 LaserDisc / CD Player [and further thoughts on the importance of objectivity]

Okay everyone... For this week, let's go old skool! Feast your eyes on this baby:

Notice the microphone input to the right - karaoke, of course...

That, friends, is the Sony MDP-750, a "vintage" LaserDisc (LD) player manufactured in February 1994 "Made in Japan" according to the label on the back. My dad bought this unit when I was still in university.

In 1994, S. Africa held interracial elections and Mandela won. The IRA declared a cease-fire in Northern Ireland. Kurt Cobain committed suicide. ER and Friends debuts on TV. Doom became a hit videogame launching many future FPS's. W3C (World Wide Web Consortium) was founded. Netscape was founded. Yahoo was launched. The Pentium was found to have some flaws in math calculations! Of course, who can forget? O.J. Simpson gets arrested for murder charges after driving around L.A. in his white Bronco. My, how time flies!

Although my family had owned a couple other CD players before this device, all the previous optical media machines have since died. This machine is built like a tank (weighing in at >21lbs) and still plays LaserDiscs like a champ! I opened it up to check on the gears and cleaned up some dust accumulated over the years.

Still got a few music LD's in the archive...

I've heard over the years that LD players are supposed to be excellent CD players on account of having a more robust transport mechanism - "over engineered" when used for CD playback. Well, based on the fact that this is the only player I have from that era purchased first hand that still works well (still plays, no weird CD tracking issues), I guess this might be true. Of course, remember that these LD players were not cheap back in the day so perhaps that translated to better build quality and materials. I can't be sure but I vaguely remember my dad spending around CAD$700-800 for this unit back then when new (BTW, it's interesting to see that the USD:CAD exchange rate today around 0.75 is almost exactly the same as it was in 1994 after going through some gyrations in the last few decades). Of course, with inflation, $700 works out to about $1100 these days.

Out back we have standard RCA stereo audio outputs, composite video, and S-Video (remember those?). This was also the first digital player the family owned with TosLink digital output... I remember the first time I played DTS audio at home to my early digital receiver was with this machine and a rental copy of Kevin Costner's Waterworld. Ahhh... The memories :-). The old remote control still works well.

Notice also the included 2-pin 18AWG power cable. Seems thin and skimpy; the kind of wire you'd find in a $25 Walmart CD player these days.

1990's PCB before everything consolidated into a couple of chips as is the case these days. And you can see the edge of an old CD-R currently in the machine. No problems playing burned disks although I noticed that old TAO burn mode CDs seem to start and one can skip between tracks quicker than more modern DAO burns (look here for more info about the difference). Alas, the DAC chip(s) are hidden on the other side of the board and I didn't feel brave enough to dismantle the unit for a look (maybe the information is available in the service manual here).

And of course back in the day, every manual had to have some specifications included on the back:

Digital audio specs look pretty good - I assume the EIAJ measurements are based on Document CP-307, "Methods of Measurement for CD Players" and the accompanying "Test Disk for CD Players" (reference made here for those interested). Nice that they even listed the headphone output impedance (not great at 8-ohms).

So... How about running this machine through the measurements and see how this vintage machine performs as a CD player?

Test Setup:
-- Source = CD-R "Test Disk" with RightMark 6 test signals, 0dBFS 1kHz square wave, 16-bit J-Test, digital filter tests, etc... Burned at 16X (slowest, assuming least jittery / risk of error) using Lite-On iHAS124 SATA DVD burner, data verified on the Memorex CD-R media.

-- Measurement Chain:
Sony MDP-750 --> 6' shielded RCA --> E-MU 0404USB ADC --> shielded USB 2.0 --> Win 8.1 Laptop

Part I: 1kHz Square Wave, Impulse Response, Digital Filter Composite

Okay, as usual, let's start with some "microscopic" examination of the analogue electrical output. Here's what a 1kHz 0dBFS square wave looks like through the digital oscilloscope:

Already this is looking rather auspicious :-). Peak voltage of ~2.9V, well formed square waves, excellent channel balance. Nice and clean as it should be.

Here's the impulse response - 44kHz signal sampled at 192kHz through the ADC:

Symmetrical sinc function with the usual pre- and post-ringing. Absolute polarity maintained. A typical linear phase oversampling antialiasing digital filter is as expected... In 1994, we were not talking about things like apodizing minimum phase settings and such.

So now let's apply the "digital filter composite" and have a better look at this filter:

Not bad. As anticipated by the impulse response above, we're looking at a sharp antialiasing filter. Looking at the 19 & 20kHz sine wave signal, harmonics can be seen up around 40kHz and 60kHz with a rise in the noise floor when playing data through the DAC. Both of these clusters peaking at least 75dB below the primary signals. "Digital silence" when playing a track with no audio information shows a very quiet noise floor even with the CD spinning.

Part II: RightMark 6

Okay, let us now compare this CD player with more modern machines and DAC's:

As you can see, I have a number of machines from over the years on the chart. I kept them in chronological order... There's my Pioneer DV-588A DVD/DVD-A/SACD universal player built in 2004. The Squeezebox / Logitech Transporter was released in 2006. The TEAC UD-501 DAC from 2013. iPhone 6 2014. And finally the PonoPlayer 2015.

Although the machines were built to different price points and different purposes, we see that 16/44 audio measurements really have not changed much over the years... The 1994 Sony certainly held its own objectively but it is a tiny bit compromised in that the noise level was not able to achieve a full 16-bit dynamic range. Closer to 15.5-bits of actual resolution.

Let's drill into the data a little more. Here's the frequency response of the different devices over the years:

Compared to the other machines, notice how flat the old Sony LD/CD player's frequency response is! A result of the steep filter utilized. The only other machine that came close is the TEAC UD-501 measured with the "Sharp" PCM digital filter setting.

Not unexpectedly, the PonoPlayer with Ayre's filter setting really "breaks the mold" with it's slow and early roll-off. As discussed previously, this is probably why standard 44kHz audio can sound different than 88+kHz "high resolution" audio on this device... Not necessarily that hi-res sounds "better" or even "different" on playback, but Ayre chose to use a rather unusual filter setting for standard resolution audio resulting in high-frequency attenuation (possibly noticeable by young ears) while the frequency response would flatten out to 20kHz with higher sample rate material!

Here's the (unsmoothed) noise floor for the different machines:

Basically, the Sony (white) on the whole is noisier than the others (though the Pioneer isn't great). The Pioneer also has a spurious noise spike around 17kHz - not sure what that's about and I haven't retested it in years.

Distortion results are really tiny across the board. However, if we zoom in on the IMD+N results:

The Sony again has the highest intermodulation distortion and noise result although PonoPlayer and iPhone 6 tend towards the higher end of the pack as well.

Part III: Jitter

Okay, 16-bit Dunn J-Test playing from my 16X burned CD-R:

Hey, not bad at all! You can see that the noise floor is a little higher than other J-Test FFT's I've shown over the years on account of the Sony being noisier (normally, the noise floor around the primary signal is down below -140dB for my ADC). Typically you'll see the jitter modulation signal (embedded in the LSB) with high-resolution DACs which you don't see here on account of the fact that the player is not capable of a full 16-bit resolution. You see a pair of low level jitter sidebands (-100dB below peak signal) but otherwise it's pretty good. Minimal "skirting" around the primary 11kHz signal as well suggesting essentially insignificant level of low frequency jitter. Would you have expected this to be the case given what you might have heard from the audiophile press over the years about the horrors of jitter, especially considering that the DAC in this player is >20 years old?

Let's now have a look at the TosLink interface and jitter as the data is sent over to the TEAC UD-501 DAC:

Aha... There's some data-related jitter sidebands, especially the +/-229Hz pair on either side of the 11kHz primary signal. Realize of course that the J-Test result is a combination of the connection between the Sony and TEAC so it's possible that the result would be quite different depending on what DAC is being used and the quality of the TosLink transceiver modules. In any event, you see that that the noise floor has improved with the TEAC DAC down around -140dB as usual with this device and my measurement ADC.

As a comparison, check out the 16-bit J-Test result from the Chromecast Audio. Notice that this Sony has more prominent +/-229Hz sidebands than the inexpensive $35 Chromecast Audio, but about on par with the recent Gigabyte Z170X-Gaming 7 motherboard with TosLink output using the TEAC DAC. Empirically, TosLink appears to be the most "jittery" of digital interfaces although it provides galvanic isolation... Whether one would be able to hear the anomaly however is IMO highly unlikely unless extremely severe.

BTW: I just recently ran into this old article on J-Test measurements and no-nonsense discussion on TNT-Audio which might be a good read for those curious about the test and the various types of jitter to be aware of.

Part IV: Subjective

So how does this sound using carbon-based measurement devices (ie. my ears & brain)? I hooked the output to my Emotive XSP-1 preamp, dual monoblock XPA-1Ls, and Paradigm Signature S8v3 speakers. In a word - it sounded "clean". That's just what came to mind. Even though I know intellectually that this player is not capable of a full 16-bit resolution, it really doesn't matter because music essentially never utilizes the full dynamic range anyways... And I don't listen to music that loud to hear the hiss down at the 15th bit - remember folks, don't go deaf prematurely :-).

Ben E. King's Spanish Harlem in mono was excellent with the Sony. The precision of the channel balance placed the music precisely front-and-center. Hey, although audiophiles might use Rebecca Pidgeon's rendition of "Spanish Harlem" (The Raven on Chesky) as a well-recorded test track, Ben E.'s 1960 version was the "original". Despite the lack of a stereo "soundstage", there is nice layering of the spanish guitar, marimbas and xylophone in the mix to provide that experience of virtual "depth" that I listen for with good mono.

Sticking with oldies music, I put in Joni Mitchell's Clouds (1969). I've always enjoyed Ms. Mitchell's sweet, early folk albums. This was her first "hit" album reaching gold certification in the US. Her voice sounded innocent and sweet... Always fun listening to this early recording of "Both Sides, Now" then contrasting the voice, prosody, and overarching emotional tone with her re-recording in 2000 "weathered" with years of smoking, age, and experience in the interim. Again, I really cannot honestly fault the Sony. It sounds great down to the fine details... No problem "feeling" the plodding melancholy in the latter rendition.

A few weeks ago, I was at the VSO with Itzhak Perlman in town. Great evening of music and showcasing Mr. Perlman's endearing personality! He ended off the evening with John Williams' theme from Schindler's List (1993). I figured this would be an appropriate CD to play since it came out around the same time as this LaserDisc player itself (and Spielberg won "Best Directing" Oscar in 1994). In any event, it's a beautiful piece and the Sony handled it with grace. Nice delivery of nuances and presentation of the orchestral soundstage. Note that although I love the music, I don't think this is a great recording. There's a noise spike in the recording near 16kHz that I remember annoyed me more when I was younger and I still think it "tips" the tonality a bit too much, resulting in a "brittle" sound. The noise floor also isn't great in this recording.

Finally, I ended off listening to something new - Bonnie Raitt's latest Dig In Deep (2016). I really think this is a great collection. I like the ballads "Undone" and "The Ones We Couldn't Be". She rocks on the first track "Unintended Consequences". And the INXS remake "Need You Tonight" is a tasteful bluesy nod to one of my favourites from the late 80's. As expected, the Sony faithfully reproduces the "modern mastering" sound of a DR7 album (seriously folks, why even bother offering a mastering like this on HDTracks at 24/96 other than parting the unsuspecting music lover from his/her cash). As I have expressed in the past, my preference is less dynamic compression and more nuance - anything less than DR10 doesn't even pass the smell test for high-resolution, never mind the taste test... Thankfully I don't think the album sounds that bad - it could be worse :-(. I wish it didn't sound like Ms. Raitt was shouting so much of course. Do something - sign the anti-Loudness War petition!

Part V: Conclusions

As I end off, I must say that I was actually quite impressed by the measurements and what I hear coming out of this 22-year old machine. In essence, what we're seeing are results suggesting a very competent CD player utilizing a typical sharp antialiasing filter with really the only weakness compared to modern machines being that of a slightly higher noise floor. Of course it's possible that with age the noise floor deteriorated (unlikely based on measurements I've seen of other machines of this vintage back in the day). It's absolutely reasonable to grab an old but hopefully lightly used player like this, clean up the gears a little, Deoxit the connectors, and enjoy the excellent quality that has been there for decades...

As I discussed back in 2013, CD players started achieving a full 16-bit dynamic resolution in the latter half of the 1990s based on measurements I've seen. By 2000, a full 16-bit level of dynamic range was relatively commonplace with reputable devices. This makes sense as it correlates with the beginning of "high-resolution" audio with DVD-A and SACD becoming available around then. Obviously since then, we're seeing machines surpassing 16-bits into the "high-resolution" capabilities with some of the most accurate DACs achieving around 20-bits of dynamic range these days. There is a maximum resolution however because of thermal noise which likely would cap the maximum dynamic range achievable in room temperature to somewhere around 22-bits within the audible spectrum. (This is important because even though we can do math calculations to 32-bit and 64-bit accuracy and you'd want this with complex DSPs, there is no point using anything more than 24-bits in music playback and delivery. Obviously all those ads about 32-bit DACs is about advertising a big number rather than "deliverables" in terms of analogue output quality.)

The other result which might come as a surprise is that the jitter test result looked really quite good with CD playback even in the early 1990's with a reputable consumer brand. This speaks to the machine being capable of good internal buffering and clocking of the DAC circuitry such that timing irregularities are minimal. Jitter is noted with the TosLink S/PDIF digital interface to the external DAC but I think like usual, it's all rather academic. As you can see, the outboard TEAC UD-501 is capable of higher dynamic range thus the J-Test output demonstrates lower noise floor as expected from a higher resolution outboard DAC. If jitter were ever an audible issue, one could imagine that back in the 1990's, a digital transport using S/PDIF connected to a DAC with poor jitter rejection may have resulted in suboptimal sound quality compared to the direct CD player output. But that was a long time ago in light of technological progress and jitter hasn't really been an issue in awhile (except in some boutique brands based on old technology, usually with big sticker prices).

Alright then folks... Enough said. Off to dust off and relive the late 80's and early 90's with some old LaserDiscs. I'm pretty sure I have an old copy of Top Gun in storage somewhere (which incidentally was the first movie I heard AC3/Dolby Digital discrete surround in a home - when jealously visiting an affluent friend's place and his dad's home theater set up!).

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Final thoughts for this week... Notice that the old Playstation 1 is somehow well-liked by certain audiophiles. It's the same vintage as the Sony LD/CD player described here - released also in 1994 (at least in Japan). Awhile ago, I measured one of these PS1's (and got very similar results to Stereophile's) and in fact still have it here at home to do a direct comparison listen! Check out the measurements between my PS1 and the Sony MDP-750 first:

As far as objective measurements are concerned, there is a clear winner! The Sony MDP-750 is better as a high quality CD player. It has better noise floor (15.5-bits resolution vs. PS1 at <15-bits), the frequency response is flat compared to the PS1's rather anomalous pattern characteristic of some of the cheap CD players and non-hi-fi products (like the Nexus 7 tablet), plus distortions are lower. (Although not shown, the jitter measurements are essentially on par and I don't see it as audible in the least.)

Considering all the models of CD-playing machines out there, I am at a loss around claims that there's anything special about the PS1. In fact, I subjectively agree with my measurements that when played through the same system, the PS1 doesn't sound that special. As I noted when I first measured it, the sound isn't bad but can seem "restrained" at times (eg. Itzhak Perlman's violin appears to lack that extra bit of expressiveness). I certainly do not have the sense that the higher noise level and imprecise frequency response out of the PS1 are desirable qualities. And I don't think I lucked out with the MDP-750 as an especially good CD player as a comparison device. (And let's not forget the user interface for the PS1 with that old game controller is just terrible!)

Currently in 2016, the PS1 is still listed in Stereophile's Recommended Components as a "Class C" product - "somewhat lower-fi sound, but far more musically natural than average home-component high fidelity". Really? I agree with "lower-fi" but what does "far more musically natural than average" mean anyway?

It is with examples like this (there are others) where the subjective review process for many products appear simply idiosyncratic... A "pet project" from some reviewer(s) that gets perpetuated not for anything really special IMO, but rather his/their own emotional sentiment. Strange that somehow in audio, it's deemed acceptable for supposedly serious mainstream publications to just hang on to the opinions of one or a handful of subjective reviewers as if it's good enough. I've also seen reviewers getting upset when questioned about their opinions/claims as if perception is always accurate. (I'm not saying that some folks don't have great hearing and their subjective opinions can be useful, but then again do magazines make sure their reviewers have their hearing tested or demand a "Golden Ears" certificate? :-)

Consider some of the most useful reviews these days of engineered products. A computer motherboard or CPU review might include Office benchmarks, gameplay fps scores, single vs. multi-core scalability, overclockability measurements, memory speed tests, etc... Car reviews - we're often offered a look under the hood, acceleration parameters, braking capability, measured top speed, road-holding ability, gas mileage, engine sound level on top of subjective creature comforts... Good digital camera reviews - sensor noise level with high ISO, sensor spatial resolution, dynamic range, flash coverage, video quality, lens tests... In these hobbies, objective measurements and the understanding of what they mean in terms of actual performance is accepted without controversy as valuable in evaluating the product. If one were to criticize that a review is incomplete without specifically looking at some objective parameter, the reviewer would accept this without feeling defensive or need to justify an oversight.

Should good audio gear reviews resemble those of other engineered devices or should we be reviewing a CD player or DAC like handbags, cigars, restaurants, and wines?

As I have stated before, even though I use an example like this out of Stereophile, this magazine is at least more reasonable, do discuss varied opinions, and publish measurements compared to many others. I've seen "audiophiles" poo-poo this fact and say they never look at the measurements - I think that's unfortunate and close-minded but to each his/her own. I appreciate the time, effort, and discipline needed in providing a factual account of performance. I believe this is harder than sitting back, listening to one's favourite tunes and writing a few subjective mental notes as the primary form of sound quality evaluation. This work adds enduring value in understanding the technology and provides for fact-based comparisons - a truth that transcends the idiosyncrasies and solipsistic tendencies of the human animal. Though I agree measurements may not account for everything, after decades in audio research surely most parameters are understood! At the very least, decent measurements are a sign of a "clean bill of health" for a product. I'm obviously not impressed that the same can be said based on just subjective opinions though.

Have a great week ahead...

Hope you're all achieving hi-fidelity when needed, and of course I hope you're all enjoying the music in whatever circumstance :-).