Interesting theory Jamie about condensers vs. ribbons. That makes sense.
I've often thought that same phenomenon applies to speakers and makes
absolute polarity more audible - a speaker cone in a cabinet, especially an
acoustic suspension design, has different damping moving out vs. in. When
it moves out, the enclosure volume increases slightly. When it moves
inward, the volume decreases, causing a stiffer "spring". I guess an
infinite baffle design wouldn't have this issue.
Bruce, how many generations down is the tape that has the distortion? I
have found that RX (and other de-clippers such as Cedar) can work well if
the material is "freshly clipped", ie. 1st generation. Once a tape is
dubbed in the analog domain, frequency dependent phase shifts come into
play and can shift the phase of the clipped portions of the waveform so
that they are no longer in the highest amplitude sections. This can even
happen on 1st generation analog recordings if the record machine has a lot
of phase shift toward the ends of the spectrum (most do).
I see this all the time in my film work, where I can see the clipping, but
it is in the downward sloping portion of the waveform, instead of at the
peaks. Once this happens, de-clippers are pretty much useless. For short
sections of this type of distortion, I sometimes have luck by individually
interpolating each cycle of the waveform over the clipped portion, using
Sonic Solutions B or D type interpolations. It takes a while, but can
sometimes work quite well. I have tried this with the spectral
interpolator in RX by selecting the entire frequency range, with no
success. I have had some success with decrackling interpolators (Sonic
Solutions E-type) or RX de-crackler, but the spikes in a muted trumpet are
often mis-interpreted as crackle, and often removed, making the distortion
worse or causing low frequency artifacts, so distortion removal from a
trumpet recording, especially muted trumpet, is nearly impossible.
You can send me a short clip, maybe 5 or 10 seconds, and I can see what I
can do with Sonic B or D type interps.
[log in to unmask]
On Tue, Sep 30, 2014 at 7:07 AM, Bruce Whisler <[log in to unmask]> wrote:
> I am working with an old tape recording that has several instances of
> distortion that sound like clipping. When I view the waveform in my DAW, I
> see two things that are puzzling:
> 1. The waveform in the distorted areas is not at a higher amplitude
> than other undistorted sections.
> 2. The waveform amplitude appears to be attenuated on the negative
> side of the waveform, but not on the positive side.
> The distorted sections usually last only about a second and do coincide
> with loud high notes from a trumpet soloist. The recordings are from live
> performances in the 1970s.
> Any thoughts on what I am dealing with? I have Izotope RX 3 Advanced, and
> have had little success in repairing this particular problem with the
> Declip, Decrackle, or Declick modules. I don't think there is enough tone
> left under the distortion to effectively repair it.
> Bruce Whisler
[log in to unmask]