On Thu, 19 Jul 2012 15:13:45 +0100, Jim Lesurf
wrote:

In article , Scott Dorsey
wrote:

Consumer equipment is designed to be as cheap as absolutely possible.
--scott

My take on that is slightly different. That consumer equipment is made to
be *sold* (at a profit), not to be *used*. Some designers/makers may be
more concerned for the end-user (rather than customer) than others. But I'm
not sure price is always a good indicator...

Apologies for the lateness of my response but I've only just
subscribed to this NG and I feel that I have a useful contribution to
make...

Almost certainly cost will be a major factor (even, as in the case of
Akai's flagship GX630DBm at that time, it is only a matter of shaving
a few pence off the cost of a piece of kit priced close to 500 quid).

In this case, looking at the plots, it seems more likely (especially
so for the Pioneer DV-939A) that the analogue output stage of the DAC
or the following stages were starved of sufficient DC bias voltage to
encompass the full peak to peak swing, i.e. they were clipping the
output waveform.

The extra 5db required for the 'waveform from Hell' is pretty close
to the 6db mark (which I suspect would only just exceed that of the
_ulimate_ 'waveform from Hell') which suggests a doubling of bias
voltage over and above that required to prevent clipping at 0db.

If the 0db voltage level is, as is commonly the case, based on the
0dbm 600R reference level (775mV rms sine), The peak to peak voltage
swing requirement at +6db becomes 4.3834v. Theoretically possible to
achieve with a single ended buffer amp powered from a 5 volt rail
(quite possibly just achievable with a FET based amplifier stage).

In this case, I suspect the real culprit isn't so much the 'extra
cost of doubling the output buffer amp rail voltage' so much as a
'lack of attention to detail' since the internal comparitor reference
voltage setting can be arbitarily adjusted[1] to avoid such
interpolated excursions exceeding whatever the peak to peak clipping
level limit happens to be in the analogue output stage(s)[2].

Getting back to the order of processing of digitised vinyl recordings
(whether direct or from tape dubs), I would suggest you look at the
whole waveform and home in on suspicious peaks manually and apply
clip/pop filtering to any that are obviously pops or clicks rather
than musical transients.

Once you've cleaned up such blatent pops and clicks, scan the
waveform to determine whether or not you now have headroom for
normalisng the tracks and assess whether the gain values look
reasonable for how the level appears by eye in the waveform editor
display (it's still possible that some strong clicks may remain
without showing in the edit display).

Once you've done this, you can apply normalisation and verify that,
in bulk, the result still looks (and sounds) ok. You could home in on
any peaks to verify whether they represent musical transients or
previously missed clicks or pops.

I tend not to apply declicking to the whole recording since it can
result in distorting effects on certain musical instruments (trumpets
can be very badly mangled by this process). I find such processing is
best concentrated on the quieter parts (typically intros and outros).

Aside from very loud clicks or pops, the music in the louder parts
will mask modest scratch noise and clicks that would otherwise become
objectionable in the very quiet parts of the recording.

I don't think there are any such cleanup filters that can be trusted
to automatically de-click / de-pop / de-scratch a complete vinyl
recording in one go without risk of objectional distortions arising
from the processing but I could well be out of touch with the latest
developments in such DSP technology[3]

If you are going to attempt to apply an all-in-one cleanup process,
audition the result thoroughly before deleting the original
un-processed wav file. Talking of which, deleting such files after
producing a cleaned up version was quite common back in the day some
ten to fifteen years ago, but with the much larger disk drive
capacities now availble, there's no longer any need for such space
savings. As long as you archive the orginal wav files, you can be as
cavalier as you like with the post digitsing processing.

[1] Of course, all bets are off if the DAC chip employed offers no
such adjustment.

[2] Assuming the manufacturer isn't totally obsessed with the 0dbm
600R reference or else is prepared to adjust to this reference by
adding the extra gain required in a seperate buffer amp that is fed
from a voltage rail that will allow a peak to peak swing without
clipping.

[3] After re- researching the subject of DSP software to bypass the
Dolby decoder stage in the tape deck itself and apply the Dolby B
decoding function in software, I don't hold out much hope for any
improvements in such de-clicking software.
--
Regards, J B Good