"Iain Churches" wrote in message
ti.fi...

"Dave Plowman (News)" wrote in message
...
In article ,
Paul Stamler wrote:
The second is that it was written fifty-plus years ago, and things have
changed a lot. Modern tapes respond a lot differently from the Scotch
111 that was the norm in 1957. For example, Burstein suggests that if
3% THD is considered the overload point, 0 VU should be 6dB below that,
and will have about 1% THD. Older tapes did work like that: distortion
increased steadily until they hit the commonly-accepted overload point
of 3% distortion. Modern tapes have much lower distortion until just
below the overload point, after which the distortion level shoots up
quickly. "Harder clipping" in the modern vernacular. Modern tapes also
do a lot better at avoiding high-frequency saturation, and of course
have much greater dynamic range.

Indeed - the 'BBC' way I was taught on setting bias in the early '60s was
to increase the bias until the level peaked (using 1kHz tone) then carry
on 'till it dropped by 1 dB. Which was a reasonable compromise for the
standard tape the BBC used in those days.


Later, a 10kHz tone was used, and bias set at 3dB over peak.
This was recommeded by AGFA for PEM468.


When I worked for Rediffusion in the early seventies, there were heated
discussions between the maintenance people and the sound engineering people
as to the correct bias setting: 1dB overbias, 2dB or 3dB....we obviously
didn't have enough work to do.....The tape machines were Philips Pro 50s and
Ampex AG440s, both using Scotch 206. We finally agreed 2dB over, but we
lined up at 700Hz, not 1kHz.

Happy days....
S.
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