On 2/9/16 7:36 PM, Tom Fine wrote:
> Hi Dave:
> There's no scientific or electronics design rule limiting a tape
> machine's frequency response to 10 octaves, that I know of. However, I
> will speculate that many antique designs may have indeed had about
> that limit in practice due to the fact that they used transformers in
> the circuits, although a good transformer should be able to pass more
> bandwidth than that (including good 1950's transformers). It could
> also have been a limit of tape-head designs of that time. I can tell
> you for a fact that the Plangent Process machine has way more than 10
> octaves bandwidth, since the same heads that recover audio are also
> recovering bias (to a separate digital track). John Chester or Jamie
> Howarth will step in here, but I believe the pathway that reproduces
> the audio content on the tape may low-pass somewhere above 20khz so as
> to not recover ringing, RF or other detrimental noises that the
> original recording may have captured.
The bandwidth of the Plangent electronics is approximately 0.1 Hz to 500
kHz. There are no analog filters in the audio path. The low frequency
limit of playback response depends on the width and profile of the head
core, just like any playback machine.
Response of a record head and tape extends down to DC. Thus, the low
frequency limit of the signal recorded on tape is entirely determined by
the record electronics and the signal fed to them.
The high frequency limit of the heads we use is well above the audio
band. A mastering grade A/D converter should be able to accurately
capture any signal we can recover from tape, up to the limit of the
converter's frequency response.
If necessary, non-audio signals above 20 kHz will be removed with
digital filters -- but this is seldom required.
We try to accurately match the reproduce EQ standard used by the
original recorder. We do not attempt to replicate any deviations from
this standard which were characteristic of a particular machine. Our
goal is to deliver audio which is as close to the input signal to the
recorder as possible.