basic – Gatt's Retro Tech

I’ve enjoyed playing with the old speccy again, but whilst I can easily load up games using an Android app called PlayZX, what I couldn’t do was save anything – either a games progress, or more specifically, any BASIC program I had written.

That was until I had a brainwave and thought about Audacity, and whilst I did record the tones, they wouldn’t load back into the device

I even installed a second sound card and connected that directly to the MIC and EAR jacks on the back of my 48K – but had the same issue

After a bit of research I found a reference stating that the signal that my PC was receiving was way too low for the spectrum to “hear” when played back. I had a look around Audacity and found that there was an “Amplify” function that, when I applied, certainly increased the tones.
Playing it back this time, I noticed a change straight away, in that I could now hear the squawks and squeals of data being loaded in, and sure enough the program was found and loaded in

So, for those who want to know how I did it – then read on.

What you’ll need:

A ZX Spectrum – duh!
Preferably the Ear & Mic leads that came with a spectrum – but suitable alternatives should be fine
A suitable PC (Running Windows or Linux) or a Mac
A Sound Card that has either a “Line In” or “Microphone” port
A copy of Audacity – (Download here)

Wiring the Spectrum up for audio

This is fairly simple

Plug each cable into the back of the spectrum and into the sound card, making sure the cable in the “EAR” socket goes into the headphone socket on the sound card, and the “Mic” lead into either the Line In or Microphone jack on the soundcard

In this case the green (yes it is green) cable will go to the headphone socket on the soundcard, and the black one to the Line In / Mic socket

And that is all there is to it – just like you would have done way back then but to a tape cassette

Configuring Audacity

Now that we’re all setup on the hardware side, it’s time to get Audacity ready.

Firstly install it if you haven’t already then, once done, come back here

Ready? Good

With Audacity open, we need to ensure we have the Device toolbar showing – this can be found under the View> Toolbars menu and selecting the “Device Toolbar” option.

Now, your options may be different to mine, but essentially the 4 drop down boxes should look something like this:

Windows DirectSound
The Line In or Microphone from your soundcard
1 (Mono) Recording Channel – Not Stereo as the ZX Spectrum is Mono only
The appropriate speaker for your soundcard

And that should be it – you may find you need to play with the volume sliders above but that will vary for everyone

Our Test Program

For this test I am just going to use a the basic BASIC program that has only 2 lines

This is all we need to be able to send some data

Saving

Now, for the interesting bit.

On the Spectrum type SAVE (by pressing S) then in double quotes (SYMBOL SHIFT + P) the name of the program, eg SAVE “test1”

And press enter, you should now get this prompt:

Don’t press anything yet!
First go back to Audacity and press the Record button THEN you can press any key on the spectrum

All being well, you should see the familiar CYAN and RED bars scrolling in the border, and a brief YELLOW and BLUE before returning with this message:

In Audacity you should now see what looks like a straight line – but all being well – that line should contain some data… For now, just click the STOP button to stop the recording

Editing

In order for the Speccy to read the data that we have just recorded in Audacity we will need to amplify the recording.

To do this we need to select the recording by clicking the “Select” button to the left of the recording

Then use the menu at the top to select “Effect” > “Volume and Compression” > “Amplify…”

Which should then open a small dialog box. Simply click “Apply” here

Now in Audacity, our line should look something like this:

All that’s left to do is to trim the end off – so just use your mouse and, just after the end of the recording left click and drag to the end – then press delete to delete that “tail” to leave something like this

You can do the same at the start if you have a line that is longer than, say 0.5 seconds – it should look similar to the image above

And that is it! All being well, then this should be ready to load back into the spectrum.

Loading

So, to load it, reset the spectrum by either turning it off then on – or pressing the “N” key to display “NEW” then pressing enter

Once done, press the J key for “LOAD” and then SYMBOL SHIFT+P twice for two quotes

Then press enter – the screen will go white as it is waiting for you to press play – so in Audacity – press the play button

And now the moment of truth – all being well it should do this

Now, if you press K for LIST – your program should be back on screen and ready to RUN:

Enjoy and have fun!

When I got my C64 back in my early teens, I did what every kid back then must’ve done and put a cassette in the tape drive and typed in LOAD “” and watched the screen mesmerised by the scrolling lines of text as I waited for the game to load..

However, eventually I started looking a that blue screen and the blinking cursor and wondered what else it could do. For me I was helped on that journey of discovery from various magazines – one series in particular called INPUT.

This series didn’t have any fancy games glued to the front cover, but rather contains lines and lines of BASIC. That you had to enter.

I was hooked and after a month I decided to have a go at creating my own program. It was rather basic (pun intended) and all it did was output all the colours available on the C64, along with its name and, more importantly, that all important POKE code that went with that number…

So here I am, 30 years later – and have recreated that very same program.

For those who don’t know what this does here’s a rough breakdown

Line 10 clears the screen
Line 20 prints the text at cursor position 13
Line 30 uses PETSCII codes to create an underline to create a title
Line 40-44 print a brief description
Line 50 beings a loop that will run 16 times, starting at 0 and then stopping after the 16th run
Line 60 reads some data into variables A and A$ – we’ll come back to that
Lines 70 through 80 deal with printing the values of A and A$ as well as a demo of what that colour looked like, before repeating the loop in line 90 and moving to the next colour
lines 1000 to 1030 are DATA statements – remember line 60 where we told it to read A and A$? well that is done here – and if you look at the code, you should see a pattern – there is a paring of a number, and a word. Starting with 0 followed by “BLACK” – then “1” followed by “WHITE”.
Each time we increase A, the READ statement on line 60 will find the corresponding number in the data lines, and then assigns the word that follows it to A$ – so on the first loop, A and A$, read “0” and “Black”, on loop 2, “1” and “White”, and so on until it gets to the end of loop with A being 15 and A$ being “Light Grey”

So when we run the program we should see this:

And that was it – that was my first foray into BASIC programming on the C64.. for little ol’ me at the time – this was impressive and I quickly grabbed a spare cassette tape, put it into my datasette, and saved it to that tape.

At that point all I could think of was – Now what do I write?

Tag: basic

Using Audacity as a virtual tape deck