Hi all,
Thought I would start a thread to discuss problems and solutions relating to digitizing and restoring recordings from old tapes.
The way I see it, most important is, get a tape player that is “easy” on the old, fragile tapes.
Most cheaper units of today are like using a sledge hammer to drive in a drawing pin and also add to wow & flutter.
Recommendations as regards makes and models are welcome.
(Hope the mods don’t mind recommendations about commercial products, in this case, tape players).
The biggest problems with old, worn out tapes are:
- wow and flutter.
- generally playing too slow (normally, as opposed to playing too fast).
- drop-outs.
- bad frequency response and/or dynamics.
- stretched sections.
As to the first two, there are commercial programs available, but they cost a fortune.
(I do have access to Izotope, but in the spirit of open source, other possibilities/software options should be explored).
I have come across a Nyquist script (note, it’s version 1, still uses “s” versus track), that can analyze
wow and flutter but, it requires one to record a 3KHz “pilot tone” first.
This is not always an option.
Plugin written by Paul Schimmel, no not me, another Paul.
;nyquist plug-in
;version 1
;type analyze
;name "Wow and Flutter Visualiser..."
;action "Processing..."
;info "by Paul Schimmel"
; 3kHz BP filter
(setf s (bandpass2 s 3000 2))
; find average, use max 10s to avoid blow up, then scale and limit
(setf s (clip(scale (/ 5 (snd-fetch(snd-avg s (snd-length s 441000) (snd-length s 441000) OP-PEAK)) ) s)1))
; differentiate, rectify
(setf s (s-abs (diff (feedback-delay s (/ 1 *sound-srate*)0) s )))
; calculate average offset, use max 10s to avoid blow up
(setf offset (snd-fetch(snd-avg s (snd-length s 441000) (snd-length s 441000) OP-AVERAGE)))
; remove offset, 60 Hz lowpass filter, scale output 1 = 1% peak
(scale 365 (lowpass8 (diff s offset) 60))
The other problem of playing too slow, that is quite easily corrected, either by using the “Change Speed”
effect in Audacity if it’s constant or, using a time track to make adjustments for the duration of the audio.
To correct drop-outs, there are several options, ranging from just cutting out the bad sections, to duplicating
a section of one track for the other.
Each situation will be different.
For stretched tapes (or sections of it), doubt there are any solutions.
As for frequency response and dynamics, eq, gain and compression can go a long way.
Any thoughts/suggests/tips, etc are most welcome.