Programs stored an cassette

What for is that?
Well, today only USB-3 sticks, which count in giga bytes, are known. A multiple of 1.000.000.000 characters at the size of a fingernail.
In the past it was different. To prevent a program to vanish with the power off of a computer, you need a medium that can easily be written on and at that time it had to be magnetic. A cloud storage was not available at that time, as there was no internet (for the common people).
Floppy disks were invented, but not very common to average people. At that time they were used at computing centers with the size of eight inches. A flat square of 8". (https://en.wikipedia.org/wiki/Floppy_disk)

A cheaper solution was, at that time, magnetic tape as a cassette. The elderly ones might remember the "diskman". But before that, there was a cassette recorder like the portable desktop cassette recorder from RadioShack. (https://en.wikipedia.org/wiki/Cassette_deck)

It was obvious to connect those devices to a computer to store programs and data on tape.

If you look carefully, you detect that the phone jacks have only two contacts. Yes, it was mono!

At those days the DIN connectors were widly spread. So they were used to connect a lot of things to the computer. (https://en.wikipedia.org/wiki/DIN_connector)

3.5mm jack plug 4i

Today not everbody has a cassette recorder at his hand, but a current notebook with a headset connector will do fine. Fortunately the DIN connectors are stil available. (DIN 5 pin 180°)

So I bought a 3.5mm 4 pin phone jack with 1.8m cable on it and a DIN connector. But be aware: There are different configurations!

We need the CTIA configuration with AUX as audio in.

For the DIN plug at the TRS-80 this configuration is valid:

  1. NC
  2. GND
  3. NC
  4. L+R
  5. AUX

With this cable the notebook can store CSAVE data as WAV files and such a WAV file can be played for restoring the content.

For those of us, that like to hear that original sound, I offer a sample here: csave_a.wav

But if you own such an old cassette with some fancy game on it, then things get hot.

I, for myself, have bought a USB sound device and put the cassette into a front loading hi-fi cassette deck, featuring full electronic transport and many other things to playback the "noise". I recorded that as a WAV file and manipulated some things:

  1. Stereo to mono conversion
  2. Noise reduction
  3. Highpass filtering with 1KHz and 6db
  4. Lowpass filtering with 13KHz and 6db
  5. Normalize the amplitude to 0db

And ready is the cassette signal!

With this cable the WAV file can directly be decoded by the TRS-80 and an old game get's back to live!