Two Ampex half tracks indeed do not make a whole, and by a significant 
margin - more like 60%. A NGB stereo head, on the other hand, scans 
around 90% of the whole. Where circumstances dictate, therefore, it is a 
useful tool for retrieving a full track tape with geometrical issues 
without unduly compromising other parameters. However, a full track head 
is undoubtedly the best way of playing a full track tape in good condition.

Removal of impulsive noise can be done without compromising the 
remaining signal, if (and mark, I say if) the right tools are used 
properly. If you use inferior stuff and/or don't adjust it properly, it 
would have been far better to leave well alone. Similar remarks apply to 
hiss - I would rather have hiss than artefacts, and broadband hiss 
reduction, because of its inevitable effects on reverb tails, is best 
avoided altogether. What is best is something like Cedar NR5, where you 
can effectively equalise the hiss separately from the signal to make it 
white or pink in character, when it becomes far less annoying.

In summary, with DSP noise reduction, don't - unless you have access to 
really good tools and are prepared to put in the time to adjust them 
properly.
> On 6/4/2014 12:43 PM, Tom Fine wrote:
>> I think that one of the hardest playbacks to get right in the analog
>> domain is an old full-track music master. Odds are that the tape will
>> have problems moving uniformly past the head. I do not think one is more
>> likely to get a good reproduction using a 2-track head, so I don't
>> understand why it's done so often. Could mastering places be that cheap,
>> that they won't shell out a few hundred dollars for a tape head that
>> will be used on every full-track project? Or is it just the usual
>> ignorance and incompetence?
>
> I think it's a combination of both. "Hry, why should we spend money on 
> another head assembly (or playback machine) to reproduce an inferior 
> format (mono) that nobody wants to listen to. Especially when a stereo 
> head does just as good a job -- after all, it reads half-tracks, and 
> two halves are the same as a whole, right?"
>
> Wrong, but tell that to the bean-counters.
>
> Peace,
> Paul
>