Sound quality differences with optical outputs - why?

For years I haven´t been bothered with digital S/PDIF connections. I basically stopped using them in 2001 when I got rid of my MD deck. This deck had been connected using its RCA digital input, only because everyone was saying that these gave superior sounding results. I never actually checked out if this was true with the result that I ignored optical Toslink in-/outputs back then. But my recent encounters with the Sony MZ-R 30 and the Sony MZ-R 900 forced me to use them again - they are the only way with which I can achieve digital copies with these MD recorders. Thankfully many of my vintage portable CD players are equipped with an optical TOSLINK interface, sometimes I also bought them for this reason. With an optical cable I can connect my PCDPs to an MD recorder to create a digital copy even including trackmarks automatically set by the MiniDisc recorder.

Optical mini-Toslink on the Sony D-335

During the last few weeks I recorded roughly twelve MiniDiscs. Some were recorded with the respective CDs played back by my Sony D-465 or the Sony D-335, some were recorded with the Creative Soundblaster X-Fi HD USB as their the digital source. To my surprise the CDs copied with those two CD players sounded different to what I´m used to, it was apparent that the sound signature had been changed somehow. The ones made with my Creative sounded pristine instead. To use an analogy: recordings from my CD players sounded like a decent analogue copy while the ones from the Creative sounded like the originals. But how can this be true? In both cases I used an optical cable that transferred its data digitally, effectively creating a second original (ignoring the lossy ATRAC compression). All the digital outputs I´ve used so far are bit-perfect meaning they won´t change the digital signal in any way. I´ve confirmed this with one of my CDs from TELARC, a rare example of a DTS-recording they released some 15 years ago. Our Sony STR-DB 830 QS is able to recognize the digital signal as DTS-encoded, it doesn´t matter which device is doing the playback. So why do I hear differences between digital signals? It just doesn´t make sense.

My optical fiber cable (copyright: Philips)

The cable you can see above is the one I´ve used for all my tests involving MD recorders and my Creative. Build quality is good... the gold plated "connectors" don´t make sense of course; the signal is pure light and cannot be influenced by the conductivity of certain metals. People seem to expect it though... what the heck, it looks nice doesn´t it? Back to the question of why I´m hearing differences. The S/PDIF protocol necessary for digital Toslink transfer has several disadvantages. The most significant is that the receiver of the signal doesn´t control it, the sender does. Because of that it must synchronize its internal clock (necessary for D/A converting) to the one contained inside the signal itself which is generated by the device transmitting it. Now in case of jitter (you knew that I would mention this, didn´t you?) introduced by an unstable or polluted clock the receiver (D/A converter or MiniDisc) won´t have a stable clock reference, in effect making jitter audible upon conversion to analogue signals. Research into this subject has been going on for years, for example from members of the AES. This influence can be reduced of course by reclocking the incoming signal. Both my MiniDisc recorders do exactly that: they reclock the signal with their built-in samplerate converter, effectively creating their own clock reference. Another impermeable wall for jitter is the MiniDisc writing process itself because it is another reclocking step. All of this should in theory eliminate jitter completely. Would it be able to survive it would result in distortions not unlike those found in intermodulation distortion and in a compromised stability and clarity of the stereo image. How are my MD recorders doing this reclocking? They probably use a phase-locked loop circuit (PLL) which you can imagine as a huge flywheel averaging out speed variations. Depending on the quality and implementation of the PLL jitter reduction is more or less successful, according to an article from Soundonsound it cannot ever be eliminated completely though. Attention: even with jitter the transferred signal will always be the same, it still contains the same 0 and 1, albeit at different places (sort of).

Jitter test signal on MZ-R 900, played back by Creative Soundblaster X-Fi HD USB

Jitter test signal on MZ-R 900, played back by Sony D-465

Look at the two pictures above by clicking on one of them, then scroll through them with your mousewheel. They were created employing the Sony MZ-R 900, its analogue output recorded with my E-MU 0202 USB. I set the MD recorder into record-pause mode in order for it to serve as a D/A converter only without the result being distorted by the ATRAC encoding. In both cases I used exactly the same signal, it´s the jitter test I usually use for my vintage portable CD players. In case of the Creative it was played back by foobar2000, utilizing the WASAPI interface of the soundcard - without resampling of course. Exactly the same file (this time burned on a CD-R) was then played back by the D-465. Level matching was unnecessary since both results have the same gain. On the pictures you can see that the spread of the signal is wider with the Creative. With the signal played back by the D-465 however there are additional sidebands absent with the Creative. The example below also exhibits a noisefloor higher for roughly 1-2 dB. While I assume these tiny differences to be insignificant, they (or something else) do have an audible effect on music. Recorded from the D-465 music has an unsharp and compact image, sounding a bit bloated and less crisp. Piano for instance sounds a bit distorted while strings loose their gloss. All of this was restored to normal when the Creative was used as a digital source for recording. I even did a DBT, not only for you but also for myself to make perfectly sure that I wasn´t hallucinating these differences:

foo_abx 1.3.4 report
foobar2000 v1.1.13
2012/06/25 20:54:42
File A: D:\Coast Guard Rescue Creative.wav
File B: D:\Coast Guard Rescue D-465.wav
20:54:42 : Test started.
20:56:15 : 01/01 50.0%
20:57:00 : 02/02 25.0%
20:57:29 : 03/03 12.5%
20:57:48 : 04/04 6.3%
20:58:08 : 05/05 3.1%
20:58:26 : 06/06 1.6%
20:59:45 : 06/07 6.3%
21:00:00 : 07/08 3.5%
21:00:06 : 08/09 2.0%
21:00:41 : 09/10 1.1%
21:01:01 : 10/11 0.6%
21:01:08 : Test finished.
----------
Total: 10/11 (0.6%)

For this DBT I recorded the same track ("Coast Guard Rescue", The Perfect Storm) twice, again with the D-465 and the Creative. Level matching was unnecessary as both had the same level, they needed precise alignment of course in order for the DBT to be successful. By this example you can see that different digital sources might have an impact on sound, even when they are bit-perfect. I´ve subsequently tested several other players and their digital outputs: all my portables appear to be susceptibe to something that distorts the digital sound while still being able to transfer a bit-perfect digital signal. There was only one portable player coming closer to the clarity of the Creative transferred signal, the DE-J 725. It didn´t sound bloated but flat and uninvolving (strangeley mirroring its analogue signature). The player almost sounding like an exact clone of the Creative was my Pioneer DV-610 AV which is nothing more than a simple DVD player. Are the reasons for this jitter? Or is it something else? I´d like to know if you, dear reader, have made similar experiences. Maybe my portables do have an unstable clock source or their signal gets distorted by other factors unknown to me yet. In either case the Creative once again proves itself to be a very reliable device of high quality. Additionally a clean digital signal from the source seems to be vital for perfect sound. To all the doubters out there: a bit-perfect realtime signal doesn´t mean that it´s free from some kind of distortion! You might now think that everything is a bliss - you are mistaken there. Recording to MD with the Creative is quite tiresome, trackmarks are not transmitted and therefore I have to set them myself after recording which essentially means that I have to divide a single, 60-minutes track into several pieces. But I´m obviously not a person that loves convenience that much (Exhibit: using MD recorders) so my desire for quality usually gets the upper hand and in the end I´m rewarded with perfect sound quality from MiniDisc. Before I forget: my reviews for the MZ-R 30 and the MZ-R 900 have been done with recordings from the Creative.

Last update: 10.01.2013

The Devil is an MD Recorder: Sony MZ-R 900 Review

You might ask: "Has she gone mad now?" No, she hasn´t. But an MD Recorder can be devilish good, that´s for sure. While the recorder I wanna talk about does not come from Spain like me in the movie "The Devil is a Woman" (pictured above) it still is able to embody the typical passion spanish Latin Lovers are known for. Well, I´m not a woman known for clichés and as much as my movie partner Cesar Romero actually was born in the U.S.A I never have been in Spain... nevermind. I´d really like to write about the Sony MZ-R 900 instead which is another MD recorder. In my last article I reviewed the Sony MZ-R 30 while also explaining the several ATRAC revisions Sony did over the 19 years the MD lasted. I also tested the Wide Bit Stream capability of my Sony MZ-R 30 and much to my surprise it was able to process digital data with a bitdepth of 24 Bit through its optical line-in. There was one obstacle though: its combined A/D/D/A converter works only at a bitdepth of 16 Bit; the 24 Bit ATRAC-processing was therefore useless. But a few days ago I was lucky and bought the Sony MZ-R 900 for very little money and that particular unit behaves a bit differently. When released in 2000 it cost 350,- Euros which makes it more expensive than my MZ-R 30 (300,- €) from three years prior. During these three years a lot happened with portable MD recorders... they became incredible tiny and loaded with features.

Sony MZ-R 900 compared to a cigarette

It´s exactly as big as an MD case (except height) which poses more problems than you might think: due to its small size and light weight it will move by itself when for example the recorder is lying on a table and one pulls on the headphone cable / FiiO E6 only slightly. It feels fragile even though its build quality is astonishing nonetheless. The precision Sony assembled it with is wonderful to look at, touching the housing feels lovely. The drive however... from my MZ-R 30 I cannot hear a thing when it records or plays a MiniDisc but the MZ-R 900 is loud as hell in comparison. According to the Manual this is normal behaviour but it still betrays its manufacturing quality in my opinion. This tiny recorder contains so many new features compared to the MZ-R 30... to write them all down here would be too much. I suggest you read about them on MZ-R 900' MD Community page should you be interested in them. Features are lovely, problems are not: our Kenwood exhibits some difficulty playing MDs recorded by the MZ-R 900. It will skip in the middle of one track to the next, it will even skip entire tracks. A few seconds prior one can hear its drive working hard to maintain the reading process. I guess the DM-5090 is starting to break down because the MZ-R 30 doesn´t have any problems whatsoever with these discs. Another thing: the headphone shares its output with the line out so you have to configure which one to use in the menu of the recorder. This wouldn´t be so unnerving if the recorder would actually remember this setting - the moment you change a disc or remove power it has "forgotten" everything. From what I´ve read the successor to the MZ-R 900 (MZ-R 901) rectifies this - a wise decision, Sony!

Sony MZ-R 900 in/ outputs

The MZ-R 900 is equipped with an ATRAC 4.5 IC, an improved version of the ATRAC encoder compared to the one built into my MZ-R 30. Through higher computational accuracy Sony managed to improve distortions by roughly 3 dB while also including a feature called "Adaptive High Band Control". The latter would ideally be responsible for an extended frequency response into higher frequencies. Just like the MZ-R 30 it also has a combined A/D/D/A converter, again from Asahi Kasei. This time it´s an AK4562, according to its manufacturer capable of recording and playback of 20 Bit signals. You shouldn´t hold up your hopes too much though: the tiny MD recorder and its converter IC are manufactured with portable use in mind and Asahi Kasei rates the D/A-part of the converter having an S/R of only -93 dB. This is not even barely good enough for pure 16 Bit performance with the result that I won´t expect too much from this unit when it comes to measurments.

Sony MZ-R 900 measurments (used as a D/A converter only through its analogue output)

ATRAC 4.5 measurments with the Kenwood DM-5090 (only through its optical output)

The measurments through its analogue output reveal nothing interesting for it behaves similar to many of my vintage portable CD players. But the chart above also reveals - just as I expected - that the D/A-converter isn´t really 20 Bit, it performs at 16 Bit at best (if I ignore the missing 3.8 dB). I have to add a little explanation: its true resolution probably reaches 20 Bits - useless though when it´s swallowed by noise resulting in a far less impressive usable resolution. For the ATRAC chart I used a testsignal recording digitally made with the MZ-R 900 that was subsequently played back by the Kenwood (it´s the only MD recorder I own that sports a digital output. Its digital signal was recorded using my Creatives' optical input. THD + Noise indeed have improved for 2 dB, IMD + Noise are better as well while the Noise level is 1 dB higher. Well done Sony... (small) step by (small) step you managed to improve the codec all those years ago (irony intended). Now I just need an ATRAC 4.5 Typ-R (according to tests it´s much better) capable MD recorder and everything will be perfect. As I mentionend during my last review I had a hard time hearing differences between the original and the ATRAC encoded version - but since then I encountered some forum posts stating that there are indeed signals able to "trip" the ATRAC ICs. I might perform some tests with these signals myself in case I should be able to purchase a unit equipped with 4.5 Typ-R.

Sony MZ-R 900 detail

The MZ-R 900 sounds very well indeed. True to the title of this review it shows explosive dynamics which on occasion tend to get too harsh and forwarding, sometimes they feel contrived and aggressive. In general it prefers high frequencies instead of presenting a completely balanced soundscape while base and mids are slightly underrepresented. This leads to a sound that can be described as euphonically charming, not the truth but tasty nonetheless. Because of its well articulated treble it presents details with analytical precision; even then the highest frequencies are diminished leading to a sound that´s drier and edgier than my references. I believe all of this to be caused by its mediocre jitter peformance; high frequency jitter brightens up the sound, low frequency jitter muddies lower frequencies. To me both results are evident here. The staging is another thing: it´s not as wide and layered as it should be, dimensions are reduced a bit. Performers mixed to the center for example tend to be too distant, on the other hand everything else surrounding these performers is encapsulated in its own 'stage bubble', including reverberation. The virtual room doesn´t sound like the original, members of an orchestra seem to change their places, reverb tails don´t seem to be as long as they are on the reference. In short: it replaces the original Ambiance with its own, highly characteristic one. Timing is another thing... while high frequency agility is excellent, mids and bass are slightly slower and miss punch and snap. All of this combined creates a dynamically powerful, slightly edgy yet charming sounding machine. It certainly is superior than other MD recorders, even superior than many of my portable CD players.
One word about its headphone output: usually I don´t talk about these, in this case I´ll make an exception because it sounds so well. The sound coming out of the MZ-R 900 when the FiiO amplifies my Sennheiser HD-448 does not change from the sound of its own amplifier. I´d use it all the time... if it wouldn´t be so weak. It simply isn´t strong enough to yield enough gain with my 32 Ohms HD-448 - a shame really.

Sonic Balance:

Dynamics:

Resolution:

Stage / Ambiance:

Character:

Sony MZ-R 900 side

Sony MZ-R 900 with one of those famed white ES MiniDiscs

Concluding my review I´d like to say that I have mixed feelings about this little recorder. The finishing quality is wonderful but it´s too small for the purpose of residing on my desktop. Yeah, I´m stupid here, I know. I´m well aware that it is a portable MD recorder and that its size makes it very convenient to carry it around. But for that purpose its headphone output isn´t strong enough to power low impedance headphones convincingly. And while the sound oozes charme and explosive dynamics it can be too edgy and aggressive at times. I think that I will indeed search for a third machine to buy, maybe one that also is NetMD equipped, I don´t know. Stay tuned!

Sony MZ-R 900

Last update: 24.07.2012