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ARSCLIST  March 2020

ARSCLIST March 2020

Subject:

Re: Digitizing Varispeed Tapes

From:

Jamie Howarth <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Fri, 6 Mar 2020 15:38:31 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (60 lines)

Lou - 
The bias oscillator is a fixed oscillator that has no interest in the speed of the machine, varispeed, dragging your thumb on a flange, spilling coffee in the motor. It doesn’t care, it happily outputs a constant frequency  and what is at the record head is constant in frequency. 

“How they interact” is how the wow and flutter correction happens. The only interaction that affects the frequency of the *recorded* bias upon *playback*  is the speed of the machine -  and the frequency shifts in that recording of the bias oscillator are subject to and thereby reflect exactly the same speed variations as anything else in the audio recording - all caused by the transport. Since they were originally a fixed tone, in effect a carrier, the machine “broadcasts” its motion as in the variations of that tone. 




Please pardon the mispellings and occassional insane word substitution I'm on an iPhone

> On Mar 6, 2020, at 14:30, Lou Judson <[log in to unmask]> wrote:
> 
> Thanks Richard. My brain’s logic says it could be either way - the varispeed could alter the bias frequency, or not, depending on machine design. But of course the tape moving at a different speed would affect how the bias was recorded. I guess I was wondering if the bias changed, and the tapespeed changed, how they would interact when using bias for wow/flutter correction.
> 
> Kind of convoluted way of thinking, but maybe wouldn’t affect the restoration process. It’s kind of like thinking about how the nozzle shape might change the trajectory of a rocket launch - so far out of my purview that it’s merely a mental excercise. Like “rocket surgery” I am not qualified. :-)
> 
> Never mind.
> <L>
> Lou Judson
> Intuitive Audio
> 415-883-2689
> 
>> On Mar 6, 2020, at 10:53 AM, Richard L. Hess <[log in to unmask]> wrote:
>> 
>> Hi, Lou,
>> 
>> It is not irrelevant, but think of what happens to a 1.5 kHz tone when you slow down on record. The wavelength gets shorter, When you play it back at normal speed, the wavelengths are still shorter so they play back at a higher frequency/pitch. The bias behaves the same except at a 100 times higher frequency / shorter wavelength.
>> 
>> I think Jamie was saying he has a feature in the software over and above the biaa capture/decoding that sounds very much like what one can do in Samplitude/Sequoia or iZotope as I described, but it's digitally programmable with inflection points, probably best handled by counting samples from the start.
>> 
>> So the challenge with using Jamie's solution IF YOU ARE THINKING OF THE BIAS CAPTURE is that it will undo the varispeed on the original recording which may or may not be what is needed.
>> 
>> I still don't fully understand the production intent of this and the OP is getting back to Jamie and me and a couple of others with more detail.
>> 
>> Cheers,
>> 
>> Richard
>> 
>>> On 2020-03-06 1:07 p.m., Lou Judson wrote:
>>> I possibly irrelvant question: Does the bias frequency stay the same when varispeeding on record? Or does it vary with the varispeed?
>>> <L>
>>> Lou Judson
>>> Intuitive Audio
>>> 415-883-2689
>>>> On Mar 6, 2020, at 9:57 AM, Jamie Howarth <[log in to unmask]> wrote:
>>>> 
>>>> Richard’s points are as always right on.
>>>> If it’s ever of help Plangent has a high quality digital non-real time algorithm for resampling that is programmable to any curve necessary to achieve the results you are asking about. It’s a service of course but I offer it where the desire is not to make another tape generation copy.
>>>> If we can help let me know.
>>>> 
>>>> Jamie Howarth
>> 
>> -- 
>> Richard L. Hess                   email: [log in to unmask]
>> Aurora, Ontario, Canada                             647 479 2800
>> http://www.richardhess.com/tape/contact.htm
>> Track Format - Speed - Equalization - Azimuth - Noise Reduction
>> Quality tape transfers -- even from hard-to-play tapes.
>> 

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