Floppy Audio!

A project log for Floppy-bird

Use a floppy-disk as a multi-frame-buffer, store audio-samples, and increase capacity to boot!

eric-hertzEric Hertz 02/07/2020 at 22:174 Comments

Updates at bottom...

Har Har Har

It's kinda funny, really... basically just storing an URL. Sure, why not, eh?

Kinda makes me ponder how many such *tiny* pieces of information might be useful in separate containers like this.

On another note: I should maybe consider breaking this up into two separate projects. 

Audio-storage is the first plan, and pretty much always has been. The original plan was to store it in analog, maybe even using an old cassette player for the electronics.

This project-idea came around a bit more like a laserdisc; wherein the audio samples themselves are analog [in value] but discrete in time. I kinda dig that concept; it's quite a rare merge of the analog->digital crossover era. 

The only other such example I'm aware of is an analog delay chip, often used in audio effects [e.g. echo]; it stores analog samples in a line of capacitors, and passes them down the line. A bucket-brigade of sample-and-hold circuits.

I take that back, actually the concept is still quite common, e.g. CCD[?] camera sensors; a discrete number of pixels, yet the pixels themselves are analog.

But, for long-term storage? Laserdiscs is all I can think of.


Storing audio on floppies is well-thought-out 'round this project; one of the bigger issues is how to playback in realtime without a noticeable skip every 1/5th second during track-change.

This project has been about how to use *unmodified* floppy drives in new ways; but that's a bit limiting for the original project idea of storing audio.

Here's a just-now new idea toward that end which doesn't fit this project:

Read/write heads have a "tunnel-erase" head. The idea is to have an empty/blank "track" between each data track so that two data tracks don't overlap. So whenever data is written, immediately after the write-head writes that data, the slightly-shifted "tunnel erase" heads erase the edges of the newly written data.

Now: with microstepping of the track motor, data [audio] could be written in a spiral. And if those tunnel-erase heads could be *read,* [especially if they're wired separately!] then we could use them to guide the microstepping during playback! Like the groove on a record. Or like a "line-following" robot. [I think CDs might do similar?]

That, though, would require floppy-drive modification; same hardware, different electronics.

And, maybe even, they could be used in different interesting ways, like storing the audio on a spirograph pattern... hmmm.

[Though, similar might be plausible with just the read-head, e.g. moving the track-motor to get the highest amplitude, especially with a carrier or *additional* wave, hmmm]

Heh, here's a weird idea, a wave outside hearing range, constant amplitude/frequency, [cassettes do this part to keep the gain during quiet parts], but, where the stored audio only contains low frequencies, the "feed" [floppy spindle motor] could be slowed! Hmmm... 


Random notes:

1 7/8 in / sec

~280 ft -> 30min/side

1500ft of groove



765 rotations / side ! 

765 "tracks"?!

Ok, maybe not re: storing an lp's worth of audio on a slow-spinning floppy, unless we slow it to 3RPM, hah! [Might be an interesting controls challenge!]


Dr. Cockroach wrote 02/09/2020 at 09:47 point

Wow, that Wiki article was packed with history and the Groove section was very interesting.

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Dr. Cockroach wrote 02/08/2020 at 10:55 point

I was wondering about a slower speed for analog as there is no conversion needed from digital to audio. Was also wondering if the floppy could be read back at a slightly faster speed than the actual audio output so that a buffer is built up and programed to account for that 1/5 sec track skip. I am just starting my morning coffee and I think you have had enough for the evening, but great thoughts :-)

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Eric Hertz wrote 02/08/2020 at 21:52 point

ahh, interesting, I hadn't thought of it being stored at a different rate. Had thought about buffering, though. Guess they'd have to go hand-in-hand...

Ah, also an interesting point; if we're hacking the spindle speed anyhow, then it could probably go *much* slower, maybe 45RPM or even 33, insteada 300. I bet a whole album-side could fit with spiral-tracks!

Wonder how difficult it'd be to keep that pancake motor at a constant velocity that slow... maybe more reason for a high-frequency synchronizer.

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Eric Hertz wrote 02/09/2020 at 00:31 point

wow, this is some interesting stuff: under "groove"

E.g., if a portion is quiet, the groove can be cut shallower, thus allowing more grooves in the same area! Also "pre-echo"/"post-echo" mitigation tactics. Interesting stuff.

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