I've played with various BAUD rate programs that allow you to save most of the RAM into a cassette tape up to around 9600 BAUD. Has anyone written or have a way to write the ram to tape (not MicroDrive) at an even faster rate? The quality is what is sacrificed, but maybe there's a better way? Thanks
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3Note that 9600 baud was already very unreliable - much to the point of unusability. Back then, I settled on about 4000 which gave me reasonable speed and failure rate (but I made sure to keep a backup with the standard speed). With something like Reed-Solomon codes, the reliability could be greatly improved, but I am afraid ZX does not have enough CPU power for this.– Radovan GarabíkCommented Apr 24, 2017 at 7:35
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1The uncertain factor is the tapes; the tape motor runs slightly slower and slightly faster from one loading to the next, tapes stretch very slightly, and signal leaks into adjacent signal. If you load from MP3 then 12000+ baud is achievable. But I guess you want a program that works on a real machine and stores (retrievably, for a prolonged period) to tape?– TommyCommented Apr 24, 2017 at 11:34
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Does MP3 (Lossy compression!) really manage to maintain this high bitrate without distorting the signal to oblivion? It's based on psychoacoustic model, to make the signal sound the same to human ear, not to retain data accuracy!– SF.Commented Apr 24, 2017 at 11:50
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1@SF yes, per code.google.com/archive/p/otla (and mrpjevans.com/2013/04/load-zx-spectrum-games-in-seconds as to the former referring only to 'MP3 players', which usually also play uncompressed audio: "yes, MP3 really works!"). It's always possible that they implemented a custom compressor that doesn't apply a psychoacoustic model, of course, but rather strips based on, ummm, Spectrum acoustics.– TommyCommented Apr 24, 2017 at 13:04
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2@Tommy The key step in the MP3 psychoacoustic model AIUI is the transformation into frequency space and the removal of small signals close (in frequency) to much larger signals. Since all microcomputer tape formats rely on a very small number of distinct frequencies (usually two), such small signals would very likely be due to errors or distortion anyway. Therefore MP3 should and does work fine with those formats.– lobCommented Jan 11, 2021 at 6:43
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1 Answer
Yes, the people at the OTLA project. More specifically, Antonio Villena wrote the "CargandoLeches" set of routines and a modified ROM that allows a Spectrum to load programs at a minimum of 11kbps, for tape, and to about 27kbps, if using audio from a digital source.
answered Apr 24, 2017 at 16:27
