There are 8 messages in this issue.
Topics in this digest:
1a. Re: Introduction and a question - windshield theory
From: madl74
2a. Question about 44.1 vs 96 kHz
From: J. Charles Holt
2b. Re: Question about 44.1 vs 96 kHz
From: sperho
2c. Re: Question about 44.1 vs 96 kHz
From: sperho
2d. Re: Question about 44.1 vs 96 kHz
From: madl74
2e. Re: Question about 44.1 vs 96 kHz
From: J. Charles Holt
2f. Re: Question about 44.1 vs 96 kHz
From: J. Charles Holt
2g. Re: Question about 44.1 vs 96 kHz
From: Bryan Celano
Messages
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1a. Re: Introduction and a question - windshield theory
Posted by: madl74
Date: Fri May 29, 2015 5:03 am ((PDT))
> Does that mean that a 6" windshield with no fur would work as well as a 4"
> windshield with a 1" layer of fur around it?
Peter,
I haven't actually measured that comparison, but I invented the soft cover
"Brinisock" and sold a couple of hundred to the BBC Film Unit in the 1960's
before Rycote took the idea up.
The problem with the original Rycote windshields was that the fine fabric
layer was on the inside of the mesh and the wind caused a hissing noise on
the mesh. My Brinisocks were actually originally designed to be rainproof as
I was working on the Police series "Softly Softly" at the time and the
schedule was so tight we had to film in all weathers and write rain into the
script.
Incidentally I got some stick from my college for making it possible to film
in pouring rain.
When I got promoted to a full Sound Recordist, I was happy for Rycote to
make a similar but not waterproof sock and they then introduced the "Hairy
Harry".
My early experimentation showed that a single thin windshield layer gives
the least alteration to the frequency response. The rule of thumb is that
any membrane or membranes should be thinner that the shortest wavelength
involved. In practice about 10mm starts to sound muffled.
There are also issues with internal reflections which alter the polar
response of gunmics, but in practice this can be tolerated in arder to get a
mic which will work in wind.
Open weave "fur" on a loose open backing parts the wind more gently as it
strikes the windshield, but the effect is to increase the effective diameter
of the whole device and thus to increase the tolerable windspeed.
David Brinicombe
Messages in this topic (8)
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2a. Question about 44.1 vs 96 kHz
Posted by: "J. Charles Holt"
Date: Fri May 29, 2015 2:47 pm ((PDT))
First off: I’m very new to this, so please bear with my likely simple question.
I got a couple recordings of a creek today using my PCM-M10 and the built-in
mics (using a Rode Dead Kitten for a windscreen). I took one at 44.1 kHz, and
another at 96 kHz just to see if I could detect any difference (expecting the
answer to likely be no). To my surprise, not only could I definitely hear a
difference, but I can also see a very obvious difference in the spectrogram
generated by Izotope RX 4. Here’s what I’m seeing (and hearing):
Screenshot of 44.1 kHz recording:
https://www.dropbox.com/s/gt1wjfqn2if06j5/Screen%20Shot%202015-05-29%20at%203.11.38%20PM.jpg?dl=0
<https://www.dropbox.com/s/gt1wjfqn2if06j5/Screen%20Shot%202015-05-29%20at%203.11.38%20PM.jpg?dl=0>
Screenshot of 96 kHz recording:
https://www.dropbox.com/s/3ej2kemhxnqei7s/Screen%20Shot%202015-05-29%20at%203.11.53%20PM.jpg?dl=0
<https://www.dropbox.com/s/3ej2kemhxnqei7s/Screen%20Shot%202015-05-29%20at%203.11.53%20PM.jpg?dl=0>
44.1 kHz recording:
https://www.dropbox.com/s/8hmjohnppq0k6eu/150529_08.WAV?dl=0
<https://www.dropbox.com/s/8hmjohnppq0k6eu/150529_08.WAV?dl=0>
96 kHz recording: https://www.dropbox.com/s/i1lg9ja125srreo/150529_09.WAV?dl=0
Note that the recordings are directly from the M10 without any editing.
Firstly, I see in the 44.1 kHz recording that the cricket sounds are creating a
very visible band at around 5 kHz with a secondary band at about 5.8 kHz. In
the 96 kHz recording, the same crickets are now two less distinct bands at 10
kHz and 15 kHz. Can someone explain to me what’s causing the apparent
compression? My expectation was just that I simply would lose the higher
frequencies with the lower sampling rate, but that doesn’t appear to be the
case.
Based on this result, my impulse is to start recording everything at 96 kHz,
file size be damned.
Messages in this topic (7)
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2b. Re: Question about 44.1 vs 96 kHz
Posted by: sperho
Date: Fri May 29, 2015 3:14 pm ((PDT))
Hi Charles,
The fundamental frequency of the cricket sound is 5 kHz. The lower amplitude
signals at multiples of the fundamental frequency are harmonics (10 and 15
kHz). The 5 kHz signal in the 96 kHz sampled spectrogram appears to be hidden
by the signal vs time-based waveform, whereas the waveform appears to be
displayed at about 3.5 kHz, allowing you to see the signal at 5 kHz. If you
can rescale the spectrogram or hide the waveform, I'm certain the 5 kHz signal
will appear. As to why there aren't any faint signals at 20, 25, 30, 40, and 45
kHz, which are all below the Nyquist frequency of 48 kHz, I would guess that
the mics aren't very sensitive at those frequencies. Given the still
reasonably visible signal at 15 kHz, I would have expected to still see a faint
signal at 20 kHz, but you won't if the mics aren't picking it up...
-Spencer
Messages in this topic (7)
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2c. Re: Question about 44.1 vs 96 kHz
Posted by: sperho
Date: Fri May 29, 2015 3:16 pm ((PDT))
Clarification:
"The 5 kHz signal in the 96 kHz sampled spectrogram appears to be hidden by
the signal vs time-based waveform, whereas the waveform appears to be displayed
at about 3.5 kHz, allowing you to see the signal at 5 kHz."
should have read,
"The 5 kHz signal in the 96 kHz sampled spectrogram appears to be hidden by
the signal vs time-based waveform, whereas the waveform in the 44.1 kHz sampled
file appears to be displayed at about 3.5 kHz, allowing you to see the signal
at 5 kHz."
Messages in this topic (7)
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2d. Re: Question about 44.1 vs 96 kHz
Posted by: madl74
Date: Fri May 29, 2015 4:07 pm ((PDT))
Charles,
I don't subscribe to Dropbox so I can't listen to the recordings. What level
were you recording at? Have you tried dropping the level by 10 or 20 dBs to
see if there are any analogue effects involved?
The digitiser input filter should be removing any HF audio near half the
sampling frequency, but an internal overload could be having an effect on
the Nyquist filter which should remove everything below half sampling
frequency.
Cricket stridulation generates a lot of ultrasound which could be upsetting
the digitising process at 44.1. It shouldn't get through, but if it does,
that would be audible. Try crunching aluminium foil for a random U/S. Play
back the recordings at a quarter or eighth speed to see if that shows
anything up.
Audio sound gear is optimised for music where much of the HF is atonal and
digital distortion difficult to hear, but wildlife follows different rules
with different spectra and different transients.
Recording low helps to avoid digital hangups and noise is not a problem so
you can usually increase the level afterwards without adding audible noise
on a live recording.
David Brinicombe
Messages in this topic (7)
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2e. Re: Question about 44.1 vs 96 kHz
Posted by: "J. Charles Holt"
Date: Fri May 29, 2015 4:38 pm ((PDT))
Spencer,
Of course, you’re correct. Once I hid the waveform, I saw the 5 kHz signal
clearly.
44.1 kHz:
https://www.dropbox.com/s/ikfvdhcgfud3d72/Screen%20Shot%202015-05-29%20at%205.24.48%20PM.jpg?dl=0
<https://www.dropbox.com/s/ikfvdhcgfud3d72/Screen%20Shot%202015-05-29%20at%205.24.48%20PM.jpg?dl=0>
96 kHz:
https://www.dropbox.com/s/8y8dytj7ik4ihvs/Screen%20Shot%202015-05-29%20at%205.25.01%20PM.jpg?dl=0
<https://www.dropbox.com/s/8y8dytj7ik4ihvs/Screen%20Shot%202015-05-29%20at%205.25.01%20PM.jpg?dl=0>
(Note that you don’t need a Dropbox account to access the files, if it asks you
to sign in just close the window)
So what I’m seeing in the 96 kHz sample are harmonics. That is much more
apparent with the complete spectrum visible!
Messages in this topic (7)
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2f. Re: Question about 44.1 vs 96 kHz
Posted by: "J. Charles Holt"
Date: Fri May 29, 2015 4:48 pm ((PDT))
David,
I read up a bit on Nyquist and believe I understand the fundamentals.
As to the comment about crickets and ultrasound, wouldn’t those higher
frequencies show up on the 96 kHz spectrogram as something other than apparent
harmonics from the 5 kHz signal? I can understanbd them not showing up at 44.1,
since the frequency response is closer to 20 kHz, but at 96 the frequency
response should be roughly doubled, correct? As I noted with Simon, you don’t
need a Dropbox account to access the files, just close the window prompting you
to sign in.
I had the record level set at 5, which to my ear is about as sensitive as I can
make the mics without getting a lot of noise. I’ve been intending to try the
pile of laundry test now that I have some software tools to get a better idea
of what’s going on (Izotope RX 4 only works in demo for 10 days, but it seems I
can still get plenty of useful information out of it indefinitely).
I’ll try the aluminum foil test and see what I get.
Thanks for the help!
– Charles
Messages in this topic (7)
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2g. Re: Question about 44.1 vs 96 kHz
Posted by: "Bryan Celano" bryanwcelano
Date: Fri May 29, 2015 4:49 pm ((PDT))
Hello,
Quick tech note on DropBox. if you change the 0 (zero) on the end to a 1
(one), it should download the file directly. If you copy/paste the link,
you'll have an opportunity to make the change.
Hope that's helpful.
Cheers!
Bryan
To:
From:
Date: Fri, 29 May 2015 17:38:05 -0600
Subject: [Nature Recordists] Re: Question about 44.1 vs 96 kHz
Spencer,
Of course, you�re correct. Once I hid the waveform, I saw the 5 kHz signal
clearly.
44.1 kHz:
https://www.dropbox.com/s/ikfvdhcgfud3d72/Screen%20Shot%202015-05-29%20at%205.24.48%20PM.jpg?dl=096
kHz:
https://www.dropbox.com/s/8y8dytj7ik4ihvs/Screen%20Shot%202015-05-29%20at%205.25.01%20PM.jpg?dl=0
(Note that you don�t need a Dropbox account to access the files, if it asks you
to sign in just close the window)
So what I�m seeing in the 96 kHz sample are harmonics. That is much more
apparent with the complete spectrum visible!
Messages in this topic (7)
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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