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Thanks for your comments Richard. I'm not surprised the Dragon NAAC is very 
slow reacting.  As you mentioned, changing azimuth manually needs to be done 
slowly to avoid adding extra timebase errors. Given the NAAC's (necessary) 
trade off  of using the one head for both detection and output, it *has* to 
be very slow reacting to maintain  stability,  at the cost of failing to 
track anything but very slow azimuth drifts or oscillations.
A more capable system would in my opinion include advance azimuth error 
information to give the slowest reacting element (the mechanical servo head 
mechanism?) the best chance of tracking faster than snail slow azimuth 
changes.

Cheers,
Tim.

----- Original Message ----- 
From: "Richard L. Hess" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, May 10, 2019 1:32 AM
Subject: Re: [ARSCLIST] Tascam 122n MK models


> Hi, Corey,
>
> It is very slow and does not respond to any once-arounds. I don't know its 
> time constants and while I think I've seen it reset during a side, I don't 
> recall seeing it often. The direction arrow on the cassette door flashes 
> while it is adjusting and I just tried it on a fairly well-recorded tape 
> and it flashes for about ten seconds at the start of playback when 
> switching from forward to reverse, which is interesting, because if  you 
> sketch it out you'll see that the azimuth error is the same on both sides 
> of the tape UNLESS this tape was recorded with a "flip-head" auto reverse 
> machine, which it very well might have been.
>
> The once-around azimuth errors are generally FAR LESS than the absolute 
> azimuth errors. See below for further commentary on ways to partially 
> ameliorate the once-around problems.
>
> Tim,
>
> The challenge with any look-ahead system is synchronization between the 
> preview head and the play head.
>
> This is why Jamie Howarth at Plangent grabs the bias signal from the play 
> head. I've gotten into long discussions with others who suggest a separate 
> read head for bias, but it will do a far inferior job of tracking 
> higher-frequency flutter components (i.e. scrape flutter).
>
> The difference between flutter and azimuth vs. groove pitch and light 
> valve protection is that as long as you make the adjustment prior to the 
> arrival of the crescendo you're protecting against, then you're fine, but 
> with instantaneous azimuth and speed, it needs to precisely track not only 
> the values but the trajectory to get it really correct.
>
> With the groove system (which I'm more familiar with than the light valve) 
> as long as you leave enough "land" for the upcoming crescendo, it doesn't 
> matter exactly where the widening occurs, and probably should occur one 
> revolution prior to the crescendo (~2 seconds) so that you've already 
> generated the wider land between the previous rotation and the "hot" one. 
> With speed and flutter the alignment might want to be within less than a 
> millisecond--if you're attacking scrape flutter perhaps an order of 
> magnitude faster than that (or even more). Azimuth might be a bit more 
> forgiving, but if you don't track the trajectory of the change you'll 
> either get ahead or behind and both are errors.
>
> Corey and Tim,
>
> As I pointed out in my ARSC 2016 presentation and AES Culpeper 2018 
> presentations, by transferring mono cassettes on stereo machines, the 
> azimuth error can be improved by time alignment of the two channels prior 
> to summing (not available with a mono head)--and this improvement is 
> substantial. The AES paper is available in the AES E-library.
>
> I am familiar with two options for this. I think Steretool is faster than 
> iZotope RX in tracking, but I'm not certain either is fast enough for the 
> once-around, though Steretool's speed is adjustable, I have not played 
> with it in regard to this. I usually keep the azimuth adjustment slow to 
> avoid other adverse effects.
>
> Remember, intermodulation when you do any adjustments on the fly is a 
> concern. That has been the major time sink for John Dyson in writing the 
> Dyson-Hess DA noise reduction module for our Noise Reduction Decoder 
> System.
>
> Cheers,
>
> Richard
>
> On 2019-05-08 7:08 p.m., Corey Bailey wrote:
>> Hi All,
>>
>> The "Look Ahead" system was (is) not only used in the disc mastering 
>> process involving audio tape but in the process of making a sound 
>> negative for film release prints as well (also a dying technology).
>>
>> The Nakamichi dragon, AFIK, does not use a look ahead tape head but a 
>> separate channel that is part of the play head. The fact that Richard 
>> Hess noted about one revolution for the auto-azimuth circuit to react is 
>> disconcerting.Even though, by design, the Dragon is chasing azimuth, I 
>> thought it would be faster than that.
>>
>> Cheers!
>>
>> Corey
>>
>> Corey Bailey Audio Engineering
>> www.baileyzone.net
>>
>> On 5/8/2019 2:45 AM, Tim Gillett wrote:
>>> Thanks Richard, that sounds like a practical use of the tools available.
>>>
>>> Thinking more conceptually about Stuart's point about a repetitively 
>>> skewing azimuth and the potential hysteresis problem, I recalled today 
>>> the old system used in disc cutting where a "look ahead" tape head would 
>>> read the volume levels of the master tape before the actual repro head 
>>> received the same signal. It gave the disc cutter lathe's lead screw 
>>> servo time to widen or narrow the groove spacing dependent on track 
>>> volume.
>>>
>>> A similar system might be used for tracking faster and repetitive 
>>> azimuth changes in a tape. A "look ahead" head gathers information about 
>>> the azimuth skew. The information - after processing - controls the 
>>> azimuth settings of a Nak Dragon style downstream read head.
>>> Since we're only interested in playback, not record, the "look ahead" 
>>> head could fit in the space previously occupied by the record head or 
>>> even the erase head. Just a thought.
>>>
>>> Cheers,
>>> Tim
>>>
>>> ----- Original Message ----- From: "Richard L. Hess" 
>>> <[log in to unmask]>
>>> To: <[log in to unmask]>
>>> Sent: Wednesday, May 08, 2019 6:58 AM
>>> Subject: Re: [ARSCLIST] Tascam 122n MK models
>>>
>>>
>>>> Hi, Tim,
>>>>
>>>> You approached Stuart's challenge from a different direction. I can 
>>>> tell you that I've received tapes that "pin" the Dragon's auto azimuth 
>>>> capability. If it's a Dragon-worthy tape, I'll readjust the mechanical 
>>>> azimuth to get some range on the motor-driven azimuth, and then put it 
>>>> back. If it's not a Dragon-worthy tape, I'll put it in an MR-1.
>>>>
>>>> Cheers,
>>>>
>>>> Richard
>>>>
>>>> On 2019-05-07 6:13 p.m., Tim Gillett wrote:
>>>>> Hi Stuart ,
>>>>>
>>>>> I've serviced a Dragon but not to test the limits of its azimuth 
>>>>> correction system. I guess we're talking about severe azimuth changes, 
>>>>> beyond what the Nak was designed to deal with. Law enforcement people 
>>>>> must have had to deal with such recordings as court evidence and who 
>>>>> knows what they may have come up with. I've read of the JBR company 
>>>>> and a modified microcassette player they pitched to forensic people. I 
>>>>> think it had a play head split into something like 12 tracks.
>>>>>
>>>>> Cheers,
>>>>> Tim
>>>>>
>>>>> ----- Original Message ----- From: "ROBINSON Stuart" 
>>>>> <[log in to unmask]>
>>>>> To: <[log in to unmask]>
>>>>> Sent: Tuesday, May 07, 2019 6:19 PM
>>>>> Subject: Re: [ARSCLIST] Tascam 122n MK models
>>>>>
>>>>>
>>>>>> I have never used a Dragon, but what I wonder when I think about is 
>>>>>> how long it takes to respond to azimuth changes? Does it for example 
>>>>>> respond fast enough to react to tapes that have country-laning 
>>>>>> issues? I have had cassettes where record issues have meant an almost 
>>>>>> constantly shifting azimuth and I wonder whether the system can 
>>>>>> correct for this or if it will end up in hysteresis always trying to 
>>>>>> seek the ideal point.
>>>>>>
>>>>>> Stuart Robinson,
>>>>>> Audio-Visual Archival Technician,
>>>>>> School of Scottish Studies Archives,
>>>>>> The University of Edinburgh
>>>>>>
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Association for Recorded Sound Discussion List 
>>>>>> [mailto:[log in to unmask]] On Behalf Of Tim Gillett
>>>>>> Sent: 07 May 2019 04:03
>>>>>> To: [log in to unmask]
>>>>>> Subject: Re: [ARSCLIST] Tascam 122n MK models
>>>>>>
>>>>>> Hi Corey,
>>>>>>
>>>>>> On a dual capstan deck, the reason it's better for azimuth stability 
>>>>>> is its uniform back tension. In a standard single capstan deck, back 
>>>>>> tension from the supply reel tends to increase as the tape plays from 
>>>>>> start to finish.
>>>>>> Changing back tension can change azimuth. An interesting complication 
>>>>>> in our situation is that the deck which originally recorded the 
>>>>>> cassette we are now playing, may not have been dual capstan, meaning 
>>>>>> its recorded azimuth may well change from start to end of tape side.
>>>>>>
>>>>>> I was in a team digitising thousands of Oral History cassettes mostly 
>>>>>> recorded on simple single capstan cassette decks. We used Tascam Mk 
>>>>>> III playback machines which, like Naks have a constant back tension, 
>>>>>> but controlled electronically, not by dual capstan. Often the azimuth 
>>>>>> alignment would slowly drift from start to end of the tape side, 
>>>>>> seemingly always in the same direction. If we'd used Naks I suspect 
>>>>>> the result would have been similar.
>>>>>>
>>>>>> Ideally, such tapes would be played in a similar deck with similar 
>>>>>> back tension changes! Or on a model such as a Dragon, but I wonder 
>>>>>> how many of us have access to one of those?
>>>>>>
>>>>>> The other thing is that it's the constant back tension which *allows* 
>>>>>> removal or lifting of the pressure pad. This means that many 
>>>>>> otherwise fine dual capstan cassette decks would potentially benefit 
>>>>>> from the adding of a pressure pad lifter, as per the Naks. I've 
>>>>>> modded a few such dual capstan decks (Pioneer, Tandberg, Sony) with a 
>>>>>> custom made pressure pad lifter with good results. It's not always 
>>>>>> appreciated that the absence of the pressure pad greatly improves 
>>>>>> head life, which is one of the main reasons I like Naks myself.
>>>>>>
>>>>>> The Tascam 122 MkIII retains the pressure pad but it mostly works 
>>>>>> againt the record head, not the play, but has a role to play in 
>>>>>> maintaining the back tension across the play head downstream of it. 
>>>>>> The pressure pad on the record head causes quite a bad wear groove 
>>>>>> after not too long a time, but in even the worst wear cases I've 
>>>>>> never seen a play head - sitting right next to the record head- worn 
>>>>>> nearly as badly or unsalvageable.( The Tascam
>>>>>> 122 head is a beautiful piece of engineering IMO, which unusually 
>>>>>> allows full adjustment of the record head independently of the play 
>>>>>> head. They're not locked together). In my view the 122 record/play 
>>>>>> head assembly should be replaced not when straight line playback 
>>>>>> performance suffers, but earlier when the record head becomes grooved 
>>>>>> due to the wear from the pressure pad..
>>>>>> This is especially so when azimuth is routinely adjusted and the tape 
>>>>>> is forced to distort inside the "tramline track" of the worn record 
>>>>>> head as the head twists with azimuth adjustments. Of course this 
>>>>>> applies to any tape head in any machine.
>>>>>>
>>>>>> I noticed on a head from a later model Nak deck, relief slots were 
>>>>>> factory cut into the head faces. A nice feature, especially in a 
>>>>>> transfer situation where azimuth is regularly being adjusted.
>>>>>>
>>>>>> Tim Gillett
>>>>>>
>>>>>> Perth,
>>>>>> Western Australia
>>>>>>
>>>>>>
>>>>>>
>>>>>> ----- Original Message -----
>>>>>> From: "Corey Bailey" <[log in to unmask]>
>>>>>> To: <[log in to unmask]>
>>>>>> Sent: Monday, May 06, 2019 11:06 AM
>>>>>> Subject: Re: [ARSCLIST] Tascam 122n MK models
>>>>>>
>>>>>>
>>>>>>> Hi John,
>>>>>>>
>>>>>>> I prefer cassette decks with a dual capstan mechanism for playback. 
>>>>>>> The
>>>>>>> reason is that cassettes, particularly old ones, tend to skew and a 
>>>>>>> dual
>>>>>>> capstan deck will hold azimuth better throughout the length to the 
>>>>>>> tape.
>>>>>>> Some Nakamichi's also have the added feature of a pressure pad 
>>>>>>> lifter. If
>>>>>>> you are going to consider a NAK, be sure and buy one that was built 
>>>>>>> post
>>>>>>> 1982. Dual capstan decks are expensive, even used which, I think, is 
>>>>>>> the
>>>>>>> only way you will find one. The Tascam that you mention is current 
>>>>>>> but a
>>>>>>> good used dual capstan machine will out perform it, hands down.
>>>>>>>
>>>>>>> My $0.02
>>>>>>>
>>>>>>> Corey
>>>>>>>
>>>>>>> Corey Bailey Audio Engineering
>>>>>>> www.baileyzone.net
>>>>>>>
>>>>>>> On 5/5/2019 7:19 AM, John Schroth wrote:
>>>>>>>> Hoping to get some input from everyone.
>>>>>>>>
>>>>>>>> I'd like to add a Tascam 122 cassette deck to our inventory. I've 
>>>>>>>> been
>>>>>>>> studying up on the different models, reading conflicting reports. 
>>>>>>>> Does
>>>>>>>> anyone have recommendations on which of the models they prefer - 
>>>>>>>> the
>>>>>>>> original 122, MK-II or MK-III?
>>>>>>>>
>>>>>>>> Thanks in advance for any input.
>>>>>>>>
>>>>>>>> Kind Regards,
>>>>>>>>
>>>>>>>> John Schroth
>>>>>>>>
>>>>>>
>>>>>>
>>>>>> ---
>>>>>> This email has been checked for viruses by Avast antivirus software.
>>>>>> https://www.avast.com/antivirus
>>>>>> The University of Edinburgh is a charitable body, registered in 
>>>>>> Scotland, with registration number SC005336.
>>>>>>
>>>>>
>>>>
>>>> -- 
>>>> 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.
>>
>
> -- 
> 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.