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Author Topic: 2mm 2-track heads or 0.75mm Stereo?  (Read 3440 times)

Offline Danny Kaey

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2mm 2-track heads or 0.75mm Stereo?
« on: April 28, 2007, 08:18:24 AM »
Hi all,

trying to figure this out... I am configuring a deck and was curious as to what heads to ask for:

2mm 2-track or 0.75mm Stereo?

From what I understand, the 2mm configuration was done to allow a for pilot tone recording in between; also, you lose a bit of S/N due to smaller recording area...

anyone know the details?

thanks!
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Offline High and Outside

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Re: 2mm 2-track heads or 0.75mm Stereo?
« Reply #1 on: April 30, 2007, 01:46:59 AM »
In audio we love standards. We love them so much we like to have at least two standards for everything.

Whenever we divide up the width of the tape for multiple channels, we don't get to use the entire width, we have to leave a little room in between tracks. This is called the guard band. We normally leave a little at the edges too. So you can see that the effective track is going to be considerably less than the theoretically available eighth of an inch per track, in the case of two channels on quarter inch.

There are two standards for the track width of two-channel heads on quarter inch tape. The one often used in Europe and referred to as the DIN standard, uses a wider track width and a narrower guard band: 0.75mm. The one used most generally in the US, the NAB standard, uses a narrower track width and a wider guard band: 2mm.  Both theory and measurement agree: with the wider track you get better signal to noise. With the wider guard band you get lower crosstalk.

And indeed the 2mm guard band does allow you to squeeze in a very narrow track for pilot tone or SMPTE time code. But I don't know whether that was the reasoning behind the spec originally. I do know you can't shoehorn that extra track into a .75mm guard band.

You can play a recording from a DIN head on an NAB playback head, or vise versa, but it's not quite optimal. One of the disadvantages stemming from having the two standards arises when a recording was made in a wide track head but recorded over on a machine with narrow track heads. The narrow track erase head might not erase everything, leaving some ghost material to show up in the new recording. This can be avoided (besides using new tape obviously, or bulk erasing used tape before re-recording) by using a full track erase head.

Here at The Tape Project we have chosen to make our tapes with NAB standard track widths. What we give up in S/N, about a dB and a fraction, is minor, and we want the lower crosstalk.
Paul Stubblebine
Managing Director, The TapeProject