Square wave on tape

[Magnus Danielson]

From: Doyle <doyle at apex.net.au>
Subject: Square wave on tape
Date: Mon, 07 Feb 2000 17:45:23 +1100

Hi Doyle!

I intentionally limited this reply to the synth-diy list...

> I recently bought  a fairly good quality rotel tape deck for $10 at the
> tip. It has all the usual features (L/R mike, Dolby NR, Bias, EQ, counter
> and VU meters..)
> It doesn't sound too good on my HiFi system (which had no line in until I
> added a socket attatched to the tape head), probably because of the
> impedence..
> ANYWAY....I decided I'd test out my Multimeter's Hz measuring and check out
> the deck at the same time....so i plugged in frequencies to the input,
> measuring them..this turned out fine...a little weak in the top area, but
> acceptable...
> SO THEN i thougt i test the distortion, so out goes the multimeter and in
> goes the scope...
> everything's fine until  i display the result of a recorded square
> wave...this was no longer square, it was a sine wave's interpretation of a
> square wave, quite smooth in fact...
> QUESTION: ((at last!) is it possible to record a square wave onto magnetic
> tape?

Well, it really depends what you call a squarewave, but sure - you can do it!

The trouble is that your oscilloscope and your waveform generator have far
more bandwidth than your tape deck, so you notice the difference ;)

Squarewave (or any other waveform) consists of a number of overtones to some
sine signal. The audio curcuits and tape head dimensions together with tape
speed will greatly contribute to strip of higher overtones. So, what you seem
to have done is to have used a fairly high frequency squarewave, so high infact
that it striped most of all overtones away for you. If you uses a lower
frequency squarewave you would get more of a squarewave on the output than
you currently get.

Cheers,
Magnus