On Sun, 07 Sep 2014 16:44:21 +0100, Jim Lesurf
wrote:
In article , Don Pearce
wrote:
On Sun, 07 Sep 2014 14:33:16 GMT, (Don Pearce) wrote:
On Sun, 07 Sep 2014 15:03:37 +0100, Jim Lesurf
wrote:
Jim, I don't know if you can watch Youtube, but here's a short clip on
the manual repair process.
So far I've not bothered with YouTube TBH.
However the problem I'm interested in is any algorithm for *finding* (and
listing the positions of) clicks and ticks. The repair is the easy part,
although I'd always do that manually so I can the waveform before and
after. Sometimes a careless repair is worse that the original. :-)
I can certainly vouch for that effect when such declicking tools are
used indiscriminately!
Like Don, I've been using CoolEdit. In my case the Pro version 1.0,
since before the turn of the century (from around 1997). I still use
it to this day but I've let the audio processing jobs stagnate these
last few years. :-(
CoolEdit Pro does have some fairly comprehensive click and pop
removal tools (and the usual noise elimination facilities as well, of
course!) but these do need to be applied with some care.
I suspect that there has been very little improvement over the past
17 years in this regard. One classic trap you can fall into is to use
automatic click removal over a whole track or even a whole LP's worth
when it contains brass wind instrumental sections since the
autodetection tends to treat this type of waveform as 'clicks'.
Indeed, this would make a nice test of the automated click removal.
Just select a section with brass (trumpets or whatever) and apply the
declicking process then compare the before and after. If you find the
processed audio is rather lacking power in the trumpet section, that
will just confirm the lack of progress I've surmised.
Like any complex tool, an audio editing program like CoolEdit, will
take some practice to get used to its limitations and to learn its
strengths (and features/foibles). I initially used it to control and
monitor the digitisation process whenever I transcribed vinyl and tape
recordings into standard wav files.
Using the older ISA soundcards (SB16, AWE64GOLD), the clip indicator
on CoolEdit's meter proved a very useful feature to let me see at a
glance whether any clipping had occurred whilst I'd had my back turned
and so alert me to the need to check and decide whether I'd have to
take another pass at a lower level (a very modest amount of real FSD
clipping was acceptable but in many cases, this could have simply been
the result of a loud pop or click in the source recording which, of
course would be excised before attempting to normalise the digital
capture).
Unfortunately, this neat clip indicator feature was defeated by the
initial crop of PCI soundcards[1] where the manufacturers it seemed,
all to a man, had slavishly followed the 'reference design' offered by
the sound chip maker and had managed to overlook the fact that
jumpering the 6dB sensitivity reduction option on the ADC had the
entirely foreseeable consequence of the input buffer amp clipping some
3dB below FSD due to reliance on the 5v line rather than a 10v
(derived from the 12v rail) source as I suspect was the case with the
older ISA cards. The aim of input noise reduction, whilst laudable
enough in its own right, unfortunately was a major error in the design
of these early PCI cards.
I soon developed a strategy for dealing with such
de-clicking/de-popping processing. Essentially, scan the whole
waveform by eye for any loud obvious spikes, home in on them to
ascertain what they actually are, select a narrow window bracketing
the click and apply the declick filter, check the result was
acceptable, undoing it if need be and try again with different
parameters or else hand edit the samples or even simpler for a very
short transient (around 1 ms or less), snip out that section entirely.
Repeat and rinse until the whole waveform was cleared of major clicks
and pops before applying normalisation (always, of course, auditioning
such edits before moving onto the next).
Usually, at that point, I'd save the wav file for further processing
later as I deemed necessary (mostly a case of cleaning up the noise
during the quieter passages, most often, during the intertrack
pauses). This basic level of processing only took 5 to 10 minutes per
album's worth so that much seemed worth doing straight away before
moving onto the next album.
Generally, I'd digitise several LP's worth per session or, in the
case of the reel to reel recordings, either both sides of a 7 inch
reel of LP tape (96 minutes per side @3 3/4 ips) or else one side of a
10 inch reel, up to 3 1/4 hours' worth.
My aim was to archive the material into a state of digital
preservation that was cleaner than if it had been auditioned
directly. Even if I never got around to any further cleanup work,
they'd still be good enough for playback. I could try improving it any
time and, that is the problem with digital media, it can so easily
induce a tendency to "Mañana". :-\
[1] For many years, I felt I was in a wilderness of 'consumers blind
to this obvious deficit' / manufacturers who didn't give a flying
****. This deficit wasn't just limited to PCI soundcards alone, even
the on-board MoBo sound chips suffered this affliction.
The situation seems to have improved somewhat over recent years, at
least as far as recently manufactured MoBos and USB adapters are
concerned. I don't know how long it took before the industry finally
spotted their "Schoolboy Howler" and corrected the design. I suspect
it took something like a decade for them to finally sit up and take
notice.
--
J B Good
Finding clicks
Linear Mode
