[music-dsp] Decibel Question - Thanks!..... and another Question :-)

James Chandler Jr. jchandjr at bellsouth.net
Tue Apr 9 13:58:06 EDT 2002


> I seem to recall that a 40dB difference usually masks the lower-power
> instrument.
> But you present an interesting case since a finger cymbal and a bass
occupy
> extreme
> opposites of the spectrum.  Intuitively it seems like the physical basis
of the
> masking effect might be that the cochlear hairs or their sensory nerves,
if
> already vibrating to a strong signal, might not readily respond to the
> lower-level one.  If you consider the rule-of-thumb that 1dB is a typical
> minimum-sensible-difference level for humans then 40dB represents a
10,000-fold
> increase in SPL!  But, if different cochlear regions respond to different
> frequency ranges (not EXACTLY TRUE, but reasonably so in the case of
greatly
> differing frequencies), it certainly is possible that the masking might
not
> occur, independent signals being transmitted to the brain for the two
> instruments.  Any thoughts?

Hi Ted

Thanks for the thoughts. Interesting thread.

Have read some about masking etc, but am pretty ignorant of the topic.

For a long time have had an old DBX 10 band RTA in-line between mixer and
monitor speakers, occasionally study the "shape" of whatever I'm listening
to.

Years ago was listening to one of the early Will Ackerman Wyndham Hill
recordings, which sounded very clear, bright, well-mixed. But it didn't
"look" bright on the RTA. Lots of lovely bright tinkly things (like finger
cymbal) happening in the highs, but the RTA showed practically no level in
the highs. Looked like a very dark mix on the RTA.

R&B and small-group Jazz recordings often sound pretty bright, though they
don't show much high freq energy on the RTA. Easy to hear brush snare or
ride-bell-ping over the rest of the mostly-low&mid-freq instrumentation.

Just from listening experience, masking does seem to be frequency specific.
Perhaps a secret to nice bright recordings is a tasteful sparse musical
arrangement. I typically decorate the top end of my recordings with egg,
tamborine, finger-cymbal, afuche type stuff, and try not to use more than
one of those instruments at any particular place in the song. But even when
the RTA is showing a pretty decent level in the highs, the mix often doesn't
sound as "bright and sparkly" as I would like. It seems quite a trick to get
this kind of "transparent bright" sound.

James Chandler Jr.




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