Looking to backup/digitise my Dad's old collection of ZX81 tapes, there's probably about 30 of them, half commercial ones and the rest self recorded. Spent the weekend rigging up an old Tandberg Audio Tutor, a converter for it's DIN output through an amplifier board, into an audio recorder. I tried out with a copy of Dice from Psion software which looked nice and short and after getting levels was able to load direct from tape, and also from the recording. I'm guessing that different tapes may need different levels...
Anyway, first of his self-recorded tapes and the loading noise is a bit different from what I expected, it also doesn't load (yet). It starts off sounding like a ZX81 but then goes a lot faster for the main section, then drops again. Here's a sample https://drive.google.com/file/d/1FF65bS ... sp=sharing (WARNING: sounds loud!)
I think from what my Dad says at the beginning of the recording: "ZXDB with fastbaud 11" might be just my ears and imagination. We did have Spectrum I think later on, along with VIC20, and I wondered if Spectrum did this, but looking on Youtube it sounds different again. Any ideas? I wonder if I might encounter more like this.
Also any pointers on the recording level constructively received.
Best wishes to all, Will
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What technique/programme do you use to process the wav file? Comparing to the original it looks like your's has been normalised and reducing the noise floor. I didn't think there was a lot about this here but I must have been using the wrong search terms bcause a lot has shown up tonight, a good thread being this one: https://www.sinclairzxworld.com/viewtopic.php?t=1014
It seems there are a few java based tools that I think automate things a bit, or processing I guess in Audacity. The programme you used to use looked like somethign intended for Spectrum games I think.
Thanks Xavier and Mark
A comparision of the machine code shows it is identical except for the displayed date and name of the cassette routine. So it appears to be an earlier version.
I don't know the history of the routine so if anyone does then I'd be keen to hear about it.
On my webpage there are details of the high speed format based on reverse engineering the code. Using this it would be possible to recover any games encoded in the format.
The filename of the program is "GMLOAD " whereas the version on my website is "RLLOAD " (note the space as the last character of both filenames).
Here are the program bytes, which exclude the filename bytes (the forum file attachment mechanism does not allow me to attach a .p81 formatted file that contains the filename bytes):
Just convert the wav to a standard 44k-16bits-mono.
Stretch the wavs to the same level, and reduce the silence level to the middle of the signal.
We can "auto-correct symmetry" on the Fastload before correct the pics levels.
The red lines at the right of the panel is the viewer of all of frequency in the file.
You had to get several red strips targeted in the same values… but in this file, there is to many noise to get a clean frequency graphic.
To clean the silent level: To set the same values on to top of the wav: FastLoad (symmetry and wavs top):
Thanks Fruitcake - the label on the tape says GMSave. My Dad is still around so I will ask him if he remembers about the techniques he used to save stuff.