Brown noise is supposed to be sleep inducing. The security folks used
pink noise in the plenum above the SCIF's to mask conversations. I
can't remember exactly what the spectrum of A-weighting was, I think it
had a dip in the mid-range.
The TV station I was employed by in college would "rent" us out to
smaller AM and FM stations who didn't have a resident engineer. The
standard AM configuration was an aggressive peak limiter followed by a
"Sta-Level" with a very long time constant. Result was the modulation
was pegged at 99.5% all the time, and it sounded that way too ... zero
dynamic range. Years ago, I looked at KFBK's waveform when the then new
Rush Limbaugh was beginning his bloviation career. It too was nearly
constant since Rush could inhale very very quickly and talked very fast.
[:-))
Non-classical FM stations [we serviced 4] used peak limiters only since
100% FM modulation is an arbitrary number [75 KHz deviation then]. The
one classical music FM station we had used no limiting/compression. Our
TV station used no limiter, NTSC aural deviation then was 25 KHz,
however our two network feeds sounded fairly well compressed.
I seem to get best audio reports, and recordings a couple of folks have
sent me sound best to me when my K3 compression reliably goes to 10 dB
with occasional peaks to 15 dB on the bar graph. Much more than that
and there's clearly room noise in pauses and the audio begins to distort.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 6/20/2019 11:15 AM, Jim Brown wrote:
Bob is correct to the extent that Pink Noise approximates the SPECTRUM
of speech, but John's is on target that speech is not continuous, but
highly variable in amplitude. For uncompressed speech, the average
value is typically as much as 20 dB below the peak value; compression
can reduce that to 10 dB or less. Highly sophisticated audio
processing that has been used by radio broadcasters for at least 40
years reduces that ratio to 6 dB or less. "If the modulation meter
moves below 100%, it isn't loud enough!"
73, Jim K9YC
On 6/20/2019 10:13 AM, John Oppenheimer wrote:
Hi Bob,
Viewing pink noise with an oscilloscope, it is continuous, where as
speech has breaks.
The web page is evaluating both expected power to a load and compression
gain. Using a little over six second recorded speech. Recording contains
fast spoken words, mostly numbers and a few "this is a test" etc, for
maximum power over time. Evaluating scope shoot, about 25 words during
six second recording. Not even close to pink noise.
John KN5L
On 6/20/19 11:27 AM, Bob McGraw K4TAX wrote:
To evaluate speech use a pink noise source. That is the standard
source signal for acoustic measurements.
Bob, K4TAX
Sent from my iPhone
On Jun 20, 2019, at 10:34 AM, John Oppenheimer <j...@kn5l.net> wrote:
Hi Don,
On 6/20/19 9:21 AM, Don Wilhelm wrote:
John,
That connection is OK if you realize that your scope is reading
the DC
voltage developed by rectifying the RF from 1/2 of the load. You
still
have to use the power formula that is in the DL1 manual.
Well yes, power references are DCV^2 / 25
DdB ratios computed using voltage ratios in the form of
20 * Log(v1/v2). For example, 0 compression Pep/Pav dB =
20 * log(15.3/5.24) = 9.3. I do need to flip the table title to
Pav/Pep
for proper negative dB values, Done.
I prefer to allow the 'scope to read the full peak RF voltage.
Connect
the 'scope probe to the side of one resistor which is connected to
the
BNC jack (one of the leads closest to the BNC), and the 'scope ground
probe to one or the resistor leads furthermost away from from the
BNC jack.
Using detected RF envelope for oscilloscope average RF measurement at
each digitized point during long, six second, trace. This will result
with increased accuracy when measuring modulated speech.
John KN5L
On 6/20/2019 9:38 AM, John Oppenheimer wrote:
Using DL1 with Oscilloscope to measure KX3 SSB RMS power:
https://www.kn5l.net/ssbpower/
Question, is this technique correct?
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