16 Oct
2024
16 Oct
'24
4:13 p.m.
On Wed, Oct 16, 2024 at 02:43:12PM +0100, Will Godfrey wrote:
There are two other factors I know of that might be
relevant.
At high tape speeds there is a drop in the replay amplitude of lower
frequencies. I believe that is due to the wavelength on the tape relative to
the width of head pole pieces. I don't know if that affects both record and
playback or just one or the other.
There are two reasons for this.
1. The NAB standard (used mainly in the USA and by Nagra at 30 IPS
speed) uses LF pre-emphasis. The actual filter used is always an
approximation of the one specified by the standard, as that one
can't exist in real life - it would require infinite gain at DC.
The actual filter used can lead to some loss at very low frequencies.
2. There is an affect depending on the physical size of the playback
head relative to wavelenght. This may results in an irregular LF response.
Both effects are perfectly linear, if they matter all you need to emulate
them is some EQ.
The background noise spectrum and amplitude changes
with different tape speeds.
I think that's related to the grain size of the magnetic particles on the tape.
The noise spectrum changes are mainly the result of the playback EQ
depending on tape speed.
Again, if the noise contributes to the 'quality' of analog tape, all
you need is to add it.
Ciao,
--
FA