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Hi Ellis,

Not exactly a polarity explanation but, I used to routinely make 
backwards copies of master tapes. The reason is: transient response. The 
heads (coils) on a tape deck can play and record transients much better 
in reverse than forwards. The trick however, was to align the repro deck 
very carefully, paying close attention to azimuth. I adopted the 
practice of using a dual-trace scope and viewing the individual tracks 
with one waveform over the other to make certain that I had adjusted for 
the best possible phase relationship between tracks. When azimuth is 
spot-on, you can overlay the two images on the scope. I only did this 
for non-Dolby masters. In fact, I rarely used any noise reduction during 
my music recording years.

Cheers!

Corey

Corey Bailey Audio Engineering

www.baileyzone.net <http://www.baileyzone.net/>



On 3/10/2015 9:03 PM, Ellis Burman wrote:
> That is the right hand rule.  Your thumb points in the direction of the
> current, and your fingers curl in the direction of the magnetic field
> around the wire.
>
> True, if a magnet is moving towards a pickup, it'll produce voltage
> opposite that of when it is moving away from it.  But I see it like Jamie
> does - N is N, + is +.  I guess I'll have to try it and prove it to myself.
>
> Kinda reminds me of the reason I've heard was to why people store tape
> tails out - so that the print through is a post echo instead of a
> pre-echo.  I never understood that one either.  It's the same distance from
> oxide layer to oxide layer, so why would it matter?  Why would the magnetic
> field have a "preference" in any direction?
>
> Ellis
>
> On Tue, Mar 10, 2015 at 2:58 PM, DAVID BURNHAM<[log in to unmask]>  wrote:
>
>    
>> 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.
>> db
>>
>>       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?
>>
>> Ellis
>>
>> On Tue, Mar 10, 2015 at 12:47 PM, Tom Fine<[log in to unmask]>
>> wrote:
>>
>>      
>>> 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?
>>>        
>>>> Was
>>>> there phase coherent tones or pink noise on all four tracks?  That seems
>>>> highly unlikely to me.
>>>>
>>>> Best,
>>>>
>>>> Ellis Burman
>>>>
>>>> On Tue, Mar 10, 2015 at 8:59 AM, Tom Fine<[log in to unmask]>
>>>> wrote:
>>>>
>>>>   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
>>>>> sucked,
>>>>> 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
>>>>> either
>>>>> 3rd or 4th generation from the transmission line). He had been smart
>>>>> enough
>>>>> 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),
>>>>> and
>>>>> 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
>>      
>>>>> of
>>>>> 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
>>>>>> have
>>>>>> a variation of at least 75-82 mils in "NAB" two track heads. At this
>>>>>> point,
>>>>>> if one is dealing with more than three tracks on 1/4-inch tapes there
>>>>>> are
>>>>>> 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
>>>>>>              
>>>>>>> 4-track
>>>>>>> and 1/4 track formats, but I'm sure more knowledgeable voices will
>>>>>>> chime
>>>>>>> in.
>>>>>>>
>>>>>>> Dave R
>>>>>>>
>>>>>>>   --
>>>>>>>
>>>>>>>                
>>>>>> Richard L. Hess                  email: [log in to unmask]
>>>>>> Aurora, Ontario, Canada                            647 479 2800
>>>>>> http://www.richardhess.com/tape/contact.htm
>>>>>> Quality tape transfers -- even from hard-to-play tapes.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>              
>>>> --
>>>> Ellis
>>>> [log in to unmask]
>>>> 818-846-5525
>>>>
>>>>
>>>>
>>>>          
>>
>> --
>> Ellis
>> [log in to unmask]
>> 818-846-5525
>>
>>
>>
>>
>>      
>
>