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Re: 0db or -8db



In a message dated 96-06-29 14:03:07 EDT, you write:

>This is one of the reasons
>that a lot of location recordists still prefer the Nagra.    When using DAT
>on
>location,  some recordists resort to working in twin track mono and
recording
>the right hand track 10db down so that there is a fair chance of avoidiing
>distortion when the dynamic range of the DAT cannot handle peak and
transient
>distortion.

I find it intriguing that there would be problems like this with DAT, which
has a dynamic range of 90 dB or better, but not with analog recorders, which
usually can't deliver more than 40-50 dB.  I know there had been some
confusion in the past regarding the set-up of digital audio recorders.
 People were calibrating them the same as analog machines, with the result
that most of the bits in the front-end ADC were "wasted" before program
level, resulting in high distortion when the ADC ran out of bits on peaks.

There are two problems with Nagra levels, at least in the U.S.  For one
thing, genuine Nagra reference tapes are very hard to come by--the one rep
that handled Nagra parts and service in the country no longer does so.
 Consequently, at least some of the people calibrating the meters on their
Nagras are using outdated or non-original reference materials.

The second problem is that none of the various PPM scales (including Nagra's)
that have been proposed around the world were ever standardized in the U.S.
 Interestingly enough, a VU meter only provides real accuracy when fed a
steady, pure sine-wave tone unless it happens to be one with "politically
correct" ballistics and calibration (the VU meters provided on most tape
machines and audio boards are a far cry from this).  On the other hand, the
meaning of reference level on a PPM scale is subject to varied
interpretation.  Strictly speaking, a true PPM meter isn't even useable with
tone, since tone has no peaks!  

As a practical matter, when the tone on a field tape is missing or is at some
bizzare level that can't be trusted, in the absence of instructions to the
contrary, a strategy that usually provides satisfactory results is to preview
the material and set the board levels so that normal conversation or speech
ends up around three dB below 0 on the VU scale.  

Christopher Bacon