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Reverse Engineering the Digital Compact Cassette

Jac Goudsmit join us to discuss one of his recent forays into reverse engineering. Plus other retro computing discussion!

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Friday, December 1, 2017 12:00 pm PST - Friday, December 1, 2017 12:30 pm PST Local time zone:
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Join this Hack Chat by clicking on the JOIN HACK CHAT button. 

____________________________________________________________

Jac Goudsmit will be hosting the Hack Chat this week.

This Hack Chat is at noon PST, Friday, December 1st. 

Time Zones got you down? Here's a handy count down timer! 

This week, we're discussing reverse engineering the audio format of Digital Compact Cassettes and other retro and not-so-retro projects. 

Digital Compact Cassettes is a magnetic tape sound recording format created by Philips and Matsushita in late 1992. It is backward compatible with all other cassette tapes that by design had the same form factor. The idea was that it would allow users to adopt digital recording using their otherwise obsolete music collections. Unfortunately, the DCC format was discontinued in 1996.

Our host, Jac Goudsmit, has been reverse engineering the audio format of digital compact cassettes. He has other retro computer projects like the L-Star, a make-your-own 6502 computer (and learn how it works).

Jac Goudsmit grew up in the Netherlands, and the first computer he ever used was a Commodore PET 2001, in around 1978. Here on Hackaday.io, Jac works on retro computer projects, software as well as hardware; original parts as well as emulation with FPGA: he maintains the P1V project, an implementation of the Parallax Propeller on several FPGA platforms.

He has a Bachelor's in Computer Science and worked on many different projects across a few industries. An interesting project was working on the application that allows audiologists to adapt hearing aids to the needs of patients at Philips Hearing Instruments.  He has worked on motion control software for ASML (lithography equipment) and Assembleon (pick and place). He even worked at Radio Shack at some point!

TL;DR Jac will be discussing a wide range of topics:

  • Differences between EE/CS careers in the Netherlands vs the USA
  • Emigrating to the United States
  • How did L-Star come about, and how does it work?
  • History of Digital Compact Cassette
  • Behind the screens of DCC: How a stereo digital PCM signal is recorded to tape
  • DCC-secrets: What is ITTS? Some info about future hacking plans

Please add your questions in the comments of this page. (thanks @naturian for the suggestion!) 

additional_transcript.txt

Transcript of the rest of the chat :) About the AUX channel, ITTS, and future possibilities of DCC.

plain - 8.08 kB - 12/01/2017 at 22:28

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  • Reverse Engineering the DCC Hack Chat Transcript

    Shayna12/01/2017 at 20:10 1 comment

    Sophi Kravitz : Let's get started with an intro about yourself from @Jac Goudsmit

    Sophi Kravitz : questions/ discussion go in the comments of the event page: https://hackaday.io/event/28313-reverse-engineering-the-digital-compact-cassette

    Jac Goudsmit : Hi everyone! I'm Jac Goudsmit, I grew up in the city of Eindhoven in the Netherlands which is where Philips (one L) comes from. I was always surrounded by Philips and I worked for them (directly or indirectly) in various places...

    Jac Goudsmit : My first job after graduating with a BSCS degree was at Codim, a small company that made CD-i productions. I wrote the software for a number of those interactive CD's for a training institute in the Netherlands called VAPRO, about processes in the industry, and I worked on background music CD's, special CD's (really CD-i's that could be played on special players) with 4 or 8 hours of background music for use in stores etc.

    Jac Goudsmit : My second job was at Philips in Hasselt, Belgium, where I worked on the embedded software for a DVB satellite receiver for the Latin American market. There I talked to several engineers who had worked on embedded software for DCC recorders

    Jac Goudsmit : Then I worked at Philips Hearing Instruments (which was taken over by Beltone while I worked there), on the Windows (3.1) software that audiologists use to adapt hearing instruments to patients' needs.

    Sophi Kravitz : @Jac Goudsmit can you tell us the basics of what the Digital Compact Cassette is?

    Jac Goudsmit : Then for a while I worked at the greatest job I ever did, in the Motion Control group of ASML, where I worked on the motion control software for the Atlas machines (later renamed TwinScan AT). Those machines have 23 degrees of freedom and each degree of freedom was updated 2000 times per second by a rack of DSP's, very complicated, very challenging. Very interesting, I truly felt like I was surrounded by genius and I learned a lot about safe C programming.

    Jac Goudsmit : Then I worked for what's now known as K&S Assembleon, on a pick-and-place machine. Also interesting but slightly lower scale: only 3 degrees of freedom :)

    Frank Buss : why would you need 23 degrees? can't you reach anything with like 6 degrees?

    Sophi Kravitz : I was going to ask something similar- what does 23 degrees mean?

    Jac Goudsmit : @Frank Buss Good question!

    Frank Buss : sounds like a snake :-)

    Jac Goudsmit : So you've probably all seen pictures of lithography machines. There's a big marble slab in the bottom, a giant 6 million dollar lens in the middle, and a reticle (basically a slide) at the top.

    There's a DUV (Deep Ultraviolet) laser as big as a desk in a room next door which shines light through the top, through the reticle, through the lens and onto the wafer that's on top of the slab.

    Jac Goudsmit : The things that our device controlled were the slab and the reticle. Each of those has an X, Y and Z.

    Jac Goudsmit : But they had a course and fine for X and Y

    Jac Goudsmit : And they also have a rotation around each axis

    Jac Goudsmit : So Slab X course/fine/rotation, Y c/f/r, Z f/r times two

    Jac Goudsmit : Then there was a device under the reticle that makes it so that only a slice of light is lit at one time, otherwise you get too much distortion.

    Jac Goudsmit : So that adds up to 20 degrees of freedom, and then there were 3 more, which are eluding me at the moment :)

    Jac Goudsmit : It's unbelievable how many things you have to take into account if you want...

    Read more »

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Discussions

Christian wrote 12/01/2017 at 20:48 point

Did DCC use any techniques for error correction (e.g. to overcome tape drop-outs)?

  Are you sure? yes | no

Jac Goudsmit wrote 12/01/2017 at 22:20 point

Yes, it uses Error detection and error correction using CIRC (just like CD). The parameters are probably different from the CD format (I don't have information about those details) but the principle is the same.

  Are you sure? yes | no

Greg Kennedy wrote 12/01/2017 at 20:11 point

Dare I ask about your opinion of DCC vs MiniDisc?  :P

  Are you sure? yes | no

Jac Goudsmit wrote 12/01/2017 at 22:01 point

I had a MiniDisc recorder in the late 1990s (until I emigrated) and I liked it very much! I liked how easy it was to do things like reorder tracks, enter track information etc. And of course it provided 74 (or so) CONTINUOUS minutes of recording time whereas DCC only had 45 minutes of continuous time until the cassette had to reverse. That made it impossible to record e.g an entire hour long radio show on one tape without interruption. And only the DCC-175 could be used to work around that: I recorded the Ben Liebrand grand mixes off the radio with two DCC recorders in 1999 (one for the first 45 minutes and one for the last half hour) and used the software to edit the recordings and put the result on a CD.

In hindsight, MD was clearly the better system, even better than CD-R which Philips came up with in the early 1990s (most consumers didn't get a CD recorder until the late 1990s but because I was involved with CD-i production I worked with CD-R much earlier). But at the time that DCC was developed, Philips thought the world needed something to record CD's in digital form, but not as fragile as DAT. They though that it would be a good idea to develop something that would be backward compatible with analog cassettes. See http://www.dutchaudioclassics.nl/?strBrand=Various&strType=InsidestoryDCC&strPage=Info for a background story.

  Are you sure? yes | no

Greg Kennedy wrote 12/01/2017 at 20:09 point

Do you have a DC-175?

  Are you sure? yes | no

Jac Goudsmit wrote 12/01/2017 at 22:03 point

Yes, I have two DCC-175s and one cable. I bought my first DCC-175 on the day they were introduced in November 1995, with a cable. It stopped working a while ago but I bought another one from eBay and that one still works. Unfortunately my 1999 Dell laptop is a bit unstable...

  Are you sure? yes | no

Greg Kennedy wrote 12/01/2017 at 20:09 point

Are you interested in this from the archivist / completionist perspective?  E.g. do you have plans to collect, catalogue, and dump DCC tapes?  Or is this mainly a technical challenge?

  Are you sure? yes | no

Jac Goudsmit wrote 12/01/2017 at 22:12 point

Personally I'm not that interested in the music on most prerecorded DCC tapes (I think @DRDCC is a bit more interested in that). Pretty much all music that was available on DCC was also available on CD and from those CD's I could record my own cassettes of course.
The reason I'm into DCC is to retain the technology. When I first saw the video by Techmoan about DCC, I realized that many people really don't even remember the format at all anymore which is a shame. What I want to do is implement some of the features that many people think Philips should have implemented, and what might have made the format more popular, such as recording your own continuous TOC, or buffering so much audio ahead that it can play a 90 minute tape without an interruption in the middle. There are indications that Matsushita may have been working on a DCC-long play format. In theory it would be possible to record a 192kbps MP3 stream with the tape running at half speed. I don't know if we ever get that far.

  Are you sure? yes | no

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