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As a medium of storing large data, cassette tapes were used just like the following:
I wonder what it would sound like if one put the tape in a cassette player and played it as if it were a regular music cassette tape. Where can I find audio footage of that?
It sounds like a high-pitched noise, somewhat like you would hear from a modem. Here's a little TRS-80 Model 1 BASIC program that plots every pixel on the screen:
10 FORY=0TO47
20 FORX=0TO127
30 SET(X,Y)
40 NEXTX
50 NEXTY
When saved on a TRS-80 Model 1, Level 1 BASIC it sounds like this:
That's 250 baud or 250 bits per second in this case. Saved under level 2 BASIC is sounds like this:
It runs at 500 baud so it sounds an octave higher. It also encodes the BASIC program a bit differently so the noise has changed.
The TRS-80 Model III can save at a blazing 1500 baud causing the program to sound like this:
Besides the pitch change the bit encoding is different. Despite it sounding like noise you can hear how it is very easy to distinguish the 3 different formats by ear.
Notice also how they all start with a quite regular sound? That's the "header" which is used to get the computer into sync with the cassette bits when it loads them. It is quite long in order to give the cassette time to get up to speed when writing.
Having used cassettes on the TRS-80 back in the early 80's I can assure you we heard that sound a lot. You wouldn't in normal operation but curiosity and practical need had us listen to the tapes. Some times to hear if a program had drop-outs or other problems that would explain why it wouldn't load. Or to locate the start of a program on tape which has multiple file saved on it. Or to figure out what baud rate to set when loading the program.
I understand this question is about the Tandy, so I'll move this to a self-answered question if necessary, but I believe you'd be interested in this information. On a ZX Spectrum (at least, the popular +2A revision with integrated Datacorder and modulated RF sound through the TV), the audio waveform on the tape is played through the TV's speakers during loading as various (unpleasant) sounds. ('Like a donkey drowning in something viscous.' it's been called.)
Because the different parts of a recorded block of data on a Spectrum tape have a uniform layout and timing, these phases not only had predictable colours on screen but also familiar tones - the result is a slowly cycling combination of constant tones, screeches and noise.
This video is the full loading of Jetpac for the Spectrum:
https://www.youtube.com/watch?v=V0EfycbDhiw
The 'pilot tone' is shown as red and cyan bars and sounds like a constant square wave. Block headers consist of a pilot tone followed by some data, so when a game begins to load, you'll hear 'beeeeep - squish' as the block is synced to then loaded.
The content of longer data blocks will have long random crunching sounds accompanied by blue and yellow dense bars as the data is loaded.
Periodic data will have its own characteristic periodic sounds while loading . This is particularly noticeable when the full content of the Spectrum screen is loaded directly -uncompressed- from the cassette into screen memory to display a title screen during the remainder of the loading process1. This memory block is sometimes called a SCREEN$ after the BASIC token representing it. A SCREEN$ has the 1bpp graphic INK data for the screen (in a non-intuitive layout of lines) first followed by the colour attribute values as a block. This means that a game title screen with a lot of repeating patterns in its graphic will have distinctive repeating whirrs, chirps, or crunches as the visual patterns are read. The attribute table also has its own unique sound since most of the screen will have repeating/common sections of colour.
Due to these effects, when a game is first loaded on a Spectrum, the initial load of the title screen has a very recognisable sequence:
then finally
Then the main game content and assets will be read as longer data blocks consisting of protracted (ten minutes upwards) continuous random harsh high pitched crunching sounds preceded by pilot beeps.
As Doc Brown would say 'Please excuse the crudity of this model.', but this is the best way I can convey it in words. :)
Further reading:
What should be the waveform for ZX Spectrum tapes?
1. You may have noticed that if it's loading directly from tape to screen memory, the Spectrum isn't doing anything else while the title screen loading is taking place. The game isn't loading in the background! A full one minute of loading is just to show a pretty picture before the real loading begins.
Aaah, who can forget James Houston's "Big Ideas: Don't get any"? The first minute is the sound of a ZX Spectrum loading its music data. Then follows three minutes of non-musical devices attempting to produce music. Frankly, I want a flatbed scanner bass myself.
It sounded a bit like this ;)
Breaking Baud is a Amstrad CPC / Schneider CPC tape loader demo by doz/crtc/3ln, which was presented on the Revision 2014.
It ranked 2nd in the oldschool category.
I had an MPF-II, one of the many Apple clones at an affordable price...
When I listened to the tapes, it was very similar to what a modem sounded like. More or less, it was taken from the same technology as the fax machine. Also back in the day, it was very slow. Modern modems & faxes can go way faster than those old computers could record on a tape.
The first phone system to transmit faxes was in 1964 by Xerox.
I had both the ZX Spectrum 48K and the Amstrad CPC 464. The audio played through the tape deck of the spectrum was like someone dragging the bow of their violin on the the 1st and the 4th string aggressively both across and up and down the fingerboard. Attuned to shaving your face from side to side instead of up or down! Painful and pointless. The Amstrad had its own cassette player attached so very rarely did you hear the code being played. But you did connect it to your phone line which was as audibly painful. Like calling a fax machine number back in the day. And just to add insult to injury 70% of the 1st time load crashed and you had to endure an extra 15-30 mins of the same screeching pain. Why the Atari 3000 cartridge console idea took so long to be replicated is mind boggling.
It doesn't sound like anything understandable by human hearing. It is basically digitalized noise, seemingly random, but still possessing a certain clean-cut quality to it that distinguishes it from a truly random white noise, and arguably makes it also much more jarring and unpleasant to listen. The closest similar thing is, imagine those digital beeps and boops, featured in movies made in nineties and before, that are supposed to telegraph a computer being busy and active. Now, imagine those beeps and boops sped up a couple dozen of times.
Screechy and grindy, basically. Like a rotary saw grinding at metal, except somehow "smoother". Not "smooth", "smoothER". Just slightly less cacophonous. Maybe like a rotary saw cutting into a church bell.
