It's not analogous to playing a record backwards. If you think of a phono cartridge, as a wave of the groove moves the stylus towards the spindle, the output will be of a certain polarity; if the stylus moves towards the edge of the record, the opposite polarity will be presented. Whether the record is playing forwards or backwards the wave towards the spindle will always be towards the spindle and the polarity won't be reversed.
With tape, however, if the tape is playing backwards, the magnetic signal on the tape will be exciting the coils in the opposite direction, causing a reverse in the polarity. You might remember from school, (if you took the same courses as I took), where they drop a magnet through a coil and an electric signal is present at the terminals of the coil. If the magnet goes through the coil in the opposite direction the signal is also in the opposite direction, plus in one direction minus in the other. I know there was a formula where if you hold up your hand with the fingers curled and the magnet travels in the direction of your thumb, the current will flow in the direction of your fingers, but unfortunately I've forgotten if it was a left hand rule or a right hand rule.
I'm sure somebody knows.
On Tuesday, March 10, 2015 4:45 PM, Ellis Burman <[log in to unmask]> wrote:
So, the same program was recorded on tracks 1 and 4?
On Tue, Mar 10, 2015 at 12:47 PM, Tom Fine <[log in to unmask]>
> Hi Ellis:
> No, I was just looking at a scope with spoken-word material on the top and
> bottom track. They were also recordings from transcription records, so
> there was quite a bit of record noise. I was surprised how many times there
> would be a loud sound at the same time for both tracks, often enough to
> verify that azimuth wasn't way off. This is inexact, to say the least, but
> everything sounded surprisingly good.
> The whole 4 tracks at once thing gets into craft vs. science.
> -- Tom Fine
> ----- Original Message ----- From: "Ellis Burman" <
> [log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, March 10, 2015 3:18 PM
> Subject: Re: [ARSCLIST] Tape dubbing backwards?
> Hi Tom. If is was a 4-track mono tape, how did you check the azimuth?
>> there phase coherent tones or pink noise on all four tracks? That seems
>> highly unlikely to me.
>> Ellis Burman
>> On Tue, Mar 10, 2015 at 8:59 AM, Tom Fine <[log in to unmask]>
>> I've never tried doing all four tracks of a quarter-track stereo of
>>> high-fidelity music all at once using my Tascam 44-OB, but I have had no
>>> problems doing some OTR (4-track mono) tapes. The quality going in
>>> so the client was very happy to save money not paying for 4 passes across
>>> the heads. I was actually surprised at how good it did sound. He told me
>>> his dubs were second-generation from transfers of transcriptions (so
>>> 3rd or 4th generation from the transmission line). He had been smart
>>> to use a good quality deck (I forgot he told me it was Pioneer or Teac,
>>> later-generation so with direct drive capstan and decent azimuth
>>> stability). On my scope, the azimuth looked OK between tracks 1 and 4,
>>> so I
>>> figured I was probably getting pretty good fidelity out of all 4 tracks,
>>> especially considering the relatively lo-fi source. His smartest moves in
>>> making the tapes were doing them at 7.5IPS and using well-slit Maxell UD
>>> tape. We also transferred at double speed (7.5IPS of 3.75IPS material),
>>> again this did not effect the sound quality of OTR source material very
>>> negatively. The guy got 4 hours of transfer material for every half hour
>>> tape machine on the clock time. As I said up front, I would never do this
>>> for high-fidelity musical recordings.
>>> -- Tom Fine
>>> ----- Original Message ----- From: "Richard L. Hess" <
>>> [log in to unmask]>
>>> To: <[log in to unmask]>
>>> Sent: Tuesday, March 10, 2015 11:49 AM
>>> Subject: Re: [ARSCLIST] Tape dubbing backwards?
>>> Some of the four-track in-line heads cheated down a little from the
>>>> standard 43 mil track width, but I think it was down to 38 mils to allow
>>>> for better crosstalk. This is not well documented...but then again we
>>>> a variation of at least 75-82 mils in "NAB" two track heads. At this
>>>> if one is dealing with more than three tracks on 1/4-inch tapes there
>>>> usually larger issues than this.
>>>> On 2015-03-09 9:09 PM, Dave Radlauer wrote:
>>>> Careful there, I don't think there's a one to one relation between
>>>>> and 1/4 track formats, but I'm sure more knowledgeable voices will
>>>>> Dave R
>>>> Richard L. Hess email: [log in to unmask]
>>>> Aurora, Ontario, Canada 647 479 2800
>>>> Quality tape transfers -- even from hard-to-play tapes.
>> [log in to unmask]
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