Storing Data to Cassette (Like it was 1975)

[@angelfire2023]

I believe the issue here is that the square wave isn't being properly reproduced. I have the DOS version of this program, and it mentions that, sometimes, one may have to use a low pass or high pass filter after recording the file from tape. I was able to encode and decode a 35kb picture perfectly, but I had to pass it through a low pass filter at 1500hz for it to decode properly due to recording it somewhat improperly. You can use your original WAV file as reference during the decoding process. Zoom in all the way to the file in audacity, and you'll see what you'll want the square wave to look like.

[@retroandgaming]

@@angelfire2023 Thanks! I've read about this but have no previous experience in signal processing but I've started to read up on low pass and high pass filters :) I'm also not too confident about my cassette player as I'm not able to load original msx software with it either. At least not reliably. But have to find the time to try this :)

[@retroandgaming]

Spent an evening with high pass and low pass filters and... no.. no joy... then my cassette recorder started to eat cassette tape.. And I noticed that it does not play back the audio at the same rate.. you can hear it going normal speed, then slower... then normal.. Next idea is to use my brand new cassette deck from Teac (W-1200)... But it's at my cabin so... need to find the time.

[@angelfire2023]

@@retroandgaming I'm sorry to hear it didn't work out. As for the tape deck, that definitely sounds like a belt issue, given it might've been sitting in that box for 35+ years untouched. The belts in tape mechs tend to seize up or begin to loosen when they aren't used for a long while (in the case of cheaply sourced belts, they may even turn to goo), and that can increase those playback issues, if not brick the unit altogether until they're replaced. A W-1200 would most certainly be far more than qualified for making data tapes with. You should be able to get a very good recording of the data signal on it so as long as the deck is in good working condition and that you record it at a proper level. Between -3db and 0db is a good range for those modern Maxell URs for recording with minimal distortion. Hopefully it works out for you if you decide to take a swing at it again. :)

[@sebastian19745]

So what is the capacity? Something around 1KB/minute? Nice try, I once tried to do the same, but FSK encoding RS232 data to tape and succesfully retrieved it. I used reel-to-reel deck at 19cm/s (4 times the speed of tape) but it did not convinced me that is a big enough medium to store data. Not tried with the old Kansas standard.

[@retroandgaming]

In my experiment the zip file was 9 580 bytes and that turned into 8 minutes and 4 seconds. So a whopping 19,8 bytes per second! Meaning that on a 90 minute tape (of course you have to split as each side is 45 minutes) you could potentially store 53 442 bytes using this implementation of KCS.

[@sebastian19745]

@@retroandgaming Thanks. So, to store more data, should 1. increase the speed and the length of the tape and of the transmission speed or 2. use another way to record data, like in the VHS. Interesting. Also, I think should need some error correction algorithm to safely retrieve the stored data even when corrupted. Anyway, 50KB is similar to 60KB of the first floppies so it makes sense that the tape was seen as an cheaper but useful alternative to floppy.

[@retroandgaming]

@@sebastian19745 yup. KCS was the first documented standard. First "attempt" was HIT. When the C64 for instance came around ~8 years later they instead of FSK (Frequency-Shift Keying) used something called Pulse length encoding. I believe the C64 was able to store about 60 bytes per second on cassette tape. I find this topic fascinating for some reason... :D

[@TrasherBiner]

Does Jarl Varg know that you plundered this from the Land to the West? If possible scan the map to the west and store it in low res in a few of those maxwell tapes. Btw , I reeeeally would have gotten a huge kick out of listening to a bit of data noise like when I loaded those zx81 games but you decided to keep it out of the video. oh well , great video otherwise. I do believe btw that in order to get accurate data you need to tweak and tune the azimuth on the take deck magnetic head (something that had to be done at the time and I coded a program back then to do this for zx spectrum). Nowadays this should be relatively trivial in python or whatever else. The reason your initial text file managed to store and retrieve identically is because it wasn't long enough to have any of the usual reading/writing errors tape recorders have. Might very well as you pointed out, be a matter of settings, but I would look into azimuthal tuning of the tape deck (it's a screw hole right over the reading/recording head when you open the tape door). I hope it helps and I loved the video, even if I couldn't help myselt to make a Norsemen referrence due to your accent.

[@retroandgaming]

He he, all of us Norwegians have an accent of sorts. No hiding that! I'm quite familiar with Azimuth tweaking from the Commodore days but I also thought that as long as I recorded with the same tape deck as I'm loading from this should have minimal effect? Might be wrong about that though. It might also be that the code is not good enough with regards to handling the introduced noise... Anyways, I might revisit this in the future but I've spent months on this already and it's time to move on to a different project for now at least :) Thx for watching!

[@TrasherBiner]

@@retroandgaming And It's a lovely accent btw (I'm not a first language English speaker either), if anything is what made me watch the video more. All it takes is a stray 1 into a 0 in a block of say, 20 Kb (even though there are measures in place for data integrity) to ruin a whole binary file. Which happened often if you lived through in the era as I did (I'd go ride my bike around the block while Manic Miner was loading only to come back home with a crashed "Micro" as you put it). As you said in the video iirc , it was a thing in the era. Btw what wouldn't I give back in 1989 for a tape deck like that , even though I had an Amstrad PC1512 (8086 clone) with 5.25" floppy at the time. It's the first thing I noticed when you opened the box "soooo fancy". it really looks like this was the pinnacle of tape technology at the time. I had 2 similar tape player/recorders in this identical format at the time (panasonic and sony) and man I nostalgia'ed so bad when I saw this and those curves compared with the standard at the time.

[@retroandgaming]

@@TrasherBiner yeah, I've been looking for a tape recorder for some time and when this showed up I did not hesitate :) It even smelled like new 80's electronics when I unboxed it. I have to see if I can find a MSX game on tape next to test if that works...

[@TrasherBiner]

@@retroandgaming oh that smell.... apparently from what I've heard that smell is not good for you, but man do I love that brand new 80's electronics smell.

[@ChadDoebelin]

try and break it up into a multipart zip file?

[@retroandgaming]

Even if you break it up you would still have to store 8 minutes to tape. And the error rate for those 8 minutes would probably be about the same. Unless you knew that certain parts of the tape where more "unstable" than others and you break it up to avoid that. There are other standards that has error correction built in so that if a bit get miss-represented this can be corrected in post-processing. But the old KCS standard did not have that.