A MiniDisc Optical Head Has A Few Surprises Up Its Sleeve

There was an odd era at the start of the 1990s when CDs had taken the lead from vinyl in pre-recorded music, but for consumer recordable formats the analogue cassette was still king. A variety of digital formats came to market to address this, of which Sony’s MiniDisc was the only one to gain significant traction outside the studio. These floppy-disk-like cartridges held a magneto-optical medium , and were the last word in cool until being swept away around the end of the decade by MP3 players. Hackaday alum [Nava Whitford] has disassembled a MiniDisc optical head to document how the physical part of the system worked.

The first surprise is that the MiniDisc was in fact a two-in-one system. The recordable discs were magneto-optical and wrote data by heating the disc with a laser under a magnetic field, while the pre-recorded discs used etched pits and lands in a similar way to the CD. Remembering the technical buzz around the system back in the day, either we audio enthusiasts glossed over this detail, or more likely, Sony’s PR did so to emphasize the all-new aspect of the system.

The teardown goes in depth into how while like a CD player there is a photodiode array involved, the extra components are a diffraction grating and a Wollaston prism, an optical component which splits polarized light into two beams. The photodiode array is more complex than that of a CD player, it’s speculated that this is to detect the different polarized beams as well as for the task of maintaining alignment with the track.

All in all this is a rare chance to look at something we know, but which few of us will probably have dismantled due to its relative scarcity compared to CD mechanisms. Definitely worth a look. Meanwhile if this era is of interest, take a look at a Hack Chat we did a while back looking at the MiniDisc’s would-be competitor.

46 thoughts on “A MiniDisc Optical Head Has A Few Surprises Up Its Sleeve

  1. I got my hands on some pro Minidisc hardware in the 2000s, and really loved the format, except for one glaring weakness. There wasn’t a way to dump the audio data to a computer. So to transfer a recording to a DAW, we had to stream it over an optical cable in real time.

      1. Probably. But it doomed the format for pro use. And ironically, doing copies in real time was pretty easy, so dumb copy protection is also worthless, as usual. :P

        1. There is a bar they set in cases like these. They know they won’t stop the professionals, skilled enthusiasts (hackers, etc.), but as long as they make it just out of reach or a pain for the masses, then they are good.

          1. These measures were not taken to thwart copying, they were done to appease upper management. It didn’t matter whether they worked or not, what was important was checking the box on the requirements memo.

          1. We used them in the theatre for audio cue playback. This was at a LORT theatre with Equity actors, meaning a professional theatre.

            So your blanket statement of “pro and compression don’t mix” isn’t just myopic it’s just plain wrong.
            Visit any professional recording studio, there are compressors. TV studio, compressors, Radio stations, compressors.

    1. It wasn’t a weakness to Sony, they considered it to be a feature. They were in a really bad place back then and made a whole lot of bone-headed moves that served no purpose other than getting people mad at them. They were lucky to survive. I think they have booted out the idiots and are back to being a normal company.

        1. I’m glad to see that I am not the only person that never buys Sony. I used to love their products but am now at about 17 years of electronics purchases without any of them being Sony.

          1. sony was not the only company to make minidisc recorders. I hadseveral Awia, ans Sharp and liked them MUCH better. I still use minidsic and wish they still msade the discs. SO much more convenient than burning CDs with the file splitting, moving, renaming, deleting, marking, etc. That couls all be done during or after recording and could be edited again and again.

      1. I still avoid any non-professional Sony gear to this day because of their boneheaded decision to include malware on CDs and their boneheaded decisions to always include some kind of model/range specific connector or protocol that was only ever useful on about 3 Sony devices and was then retired never to be seen again.

    2. Early MD gear couldn’t but later NetMD gear, with updated pc software absolutely could do this, I am a MD enthusiast myself, I even installed a MD head unit in my car. HI-MD was amazing, but unfortunately, by the time it released, it was already dead in the water, and HI-MD discs ceased manufacturing quickly, while regular MD discs are still being made new.

    3. Not officially, anyways, yeah. That was by design, and there were a few ways around it. Sony had released a SCSI MD Data drive, and some people had figured out how to dump audio discs with it. One of the later Hi-MD players (The MZ-RH1) actually officially supported getting audio tracks off of MD discs, as well. But most of the Pro gear completely ignored the copy protection flags on the discs, and would let you do optical out from any disc, which was the most “reliable” and “official” way.

    4. It was around this time that Sony bought Columbia and went from a consumer electronics company to a media ownership company and they changed the course of the MD format. They stopped selling computer MD readers/writers because those might be used to ‘pirate’ audio.

      As you point out, this cripled them in the pro market and made them less attractive even in the consumer market.

      They had been a contemporary of ZIP drives and had a lot going for them–smaller media, much more rugged media, etc., but they chose to give all that up in favor of their music/media business.

      All of this lead to the much more open CD-R format becoming dominant in the home recording and data storage world.

      1. The other thing limiting the pro use was that the audio was actually lossily compressed, in order to fit 74 minutes (one CD) on the ~60Mb capacity of one disc.

        That said, I own both an MZ-R30 (walkman-sized portable) and an MDS-M100 (fixed), which I still occasionally use. I used the portable a lot in the late 90’s for rehearsal recordings, the stereo microphone input was very good quality!

        1. Regular MiniDisc capacity is 160 MB for audio (source: https://www.minidisc.org/faq_sec_3.html).
          Sony’s ATRAC Compression was around 5:1 with a bitrate of ~280kbps.

          This is much higher than the 128kbps one would typically see in Napster or in the infancy of iTunes.

          Later versions of ATRAC (LP2 and LP4) could compress more and had a greater negative affect on sound quality.

    5. You could do it in real-time with the S/PDIF output, or with NetMD (and some ancient and dodgy software), but the copying resistance of MD was by design, and the blame can be placed squarely at the foot of the RIAA. Sony’s previous digital audio format (DAT) was successful in their domestic and in non-US markets, but was hammered into the ground in the US over fears of lossless copying with labels leant on to not support it. DAT effectively dies outside of recording studios. For MD, Sony kowtowed to the RIAA and built in copy protection, as well as buying up their own US record label (Colombia) so they had a guaranteed catalogue regardless of what the RIAA tried to pull.

  2. I think the last model released, the MZ-RH1 (a HiMD model), could do digital uploads over usb. It’s silly pricey now though and has an inevitable flaw that the two oled displays fade over time till they are not visible.

  3. About five years ago I got two MiniDisc players at garage sales, so no more than ten dollars. Mostly curiosity.

    Thefirst one doesn’t record. Or rather, no input jack. It’s intended for MP3 use, songs transferred over USB. Not so useful.

    The second is full.blown.

    I’ve yet to try them.

    I have a couple of portable CD players that can play MP3s. Another transitional device. Useful right at the beginning, but soon solid state MP3 players had more storage, and no mechanicals. I thought I got my first MP3 player late, but it had 512K memory. So about the same storage as a CD.

    1. The USB-based ones are still pretty useful. Uploading tracks to them can be done from several different modern pieces of software(Including one from Chrome). Me and a few other people have managed to dump the firmware and are in the process of working out all the hidden goodies, too.

        1. There’s a pretty active community at minidisc.wiki and the associated discord. There’s tutorials on the wiki for how to use all the various software. A lot of our findings are in the #development channel on the discord, though some of the stuff we’re keeping a bit more hidden until we have safer tools to use them.

  4. I actually just started collecting MiniDisc albums. They aren’t very common and they aren’t cheap either. But, unlike CDs or vinyl, they are well protected so rarely are they gunna be scratched up and skip. Fun hobby nonetheless.

  5. “The recordable discs were magneto-optical and wrote data by heating the disc with a laser under a magnetic field”

    I wonder how similar the mechanism was to the one Sony used in the magneto-optical drive NeXT put in the Cube.

  6. The problem with MiniDisc for me was ATRAC compression affected the sound quality quite a lot. It always sounded nicer playing from the original CDs rather than those ripped to MiniDisc.

    1. Are you talking about comparing a digital or analog transfer from CD to MD? For music copied from CD to MD via optical digital out, I could not tell a difference. This was in the 90s using a mini-system or a pair of $35 over the ear headphones for playback (so, not a high quality test setup).
      Today, even with a DAC and +$100 pair of headphones I struggle to tell a difference between a 320kbps MP3 and lossless audio such as with this test:

    1. Hi just to let u know I still have many mini disc units. Just try to erase or move a track on a CD. Increase or decrease the recording volume. Label your tracks. Sad it went away.

  7. I still have mine. I was always impressed with the quality of the device. Mine was all metal where it mattered. The hinge relied on small screws so it eventually went bad. But a bit od duct tape fixed that issue. The quality of stereo recordings was outstanding, even with the mini stereo microphone. I often fed the device with a small mixing board so I could use two decent microphones (each panned opposite) to get even richer recordings. I should dig that thing out….

  8. I still have two mini disc player/recorders and a couple hundred mini discs. Tried to sell them online but no takers. I keep thinking this might get some attention like vinyl did years ago and then I might be rich LOL

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