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2Silverman08-Noise
Low Noise
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Poster: John_Atkinson  (see this users gallery)
Views: 258
Rating: (9.00)
Date: Wed Jul 2, 2008
Filesize: 42.0k, 89.9k
Dimensions: 960 x 718
Description: When recording on location, spurious environmental noises are the biggest bugbear. Fortunately, the staff of Sauder Hall were very cooperative in helping producer Erick Lichte to track down and kill noises, including the hall's air-conditioning. As you can see from the spectrum of a rough mix of a silent passage, we were still left with some very low-frequency components: these were the rumble from a distant sewage pumping station (and its harmonics), some low-level electrical noise (which appeared to come from the lights), and even more distant traffic. They are, to all intents and purposes, inaudible. In the midrange and above, the background noise is very low indeed.


For reference, the green trace is the spectrum of the noise floor of a perfect 16-bit PCM system. In theory, it looks as if 16 bits would be sufficient to capture the piano recording's dynamic range. In practice, with real-word 16-bit digital systems, listening reveals that not to be the case.
Keywords: Low Noise


Jim Tavegia


Registered: Sep 2005
Location: Atlanta
Posts: 1157
Wed Jul 2, 2008 4:26pm Rating: 9.00 

I have never had a rig close to the low noise floor you use, but it is amazing when you put on your headphones during recording takes, what you can hear and becomes very distressing.


I have more trouble with our HVAC system(s) at church recording our Steinway. Why they put the units on the roof right next to our beautiful sanctuary is beyond me. Trying to find it and eliminate it takes cooperation...as you have found. Stuff going on across the street and next door is more problematic. Thanks for the science. I'm curious, would not the green trace be 24 bit?

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Jim Tavegia
John_Atkinson

Registered: Sep 2005
Posts: 1019
Wed Jul 2, 2008 5:00pm

>Thanks for the science. I'm curious, would not the green trace be 24 bit?<

It does look that way, Jim, but if you perform an RMS sum of all the frequency components that make up the green trace in this graph, you do end up with the -96dB noise floor typical of a 16-bit PCM system. A 24-bit system would have individual components around the -160dB level.

>Why they put the units on the roof right next to our beautiful sanctuary is beyond me.<

Probably to cut down on the ducting costs. But the mechanical noise from the compressors will then drive the roof like a large diaphragm. I had a similar problem when I recorded Cantus in Sioux Falls. The hall was permeated with an acoustic 120Hz hum. It turned out to be due to the transformers for the emergency lighting system, which were mounted above the ceiling and were vibrating it at 120Hz. :-(
Jim Tavegia


Registered: Sep 2005
Location: Atlanta
Posts: 1157
Wed Jul 2, 2008 7:24pm

Thanks for the free lesson.

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Jim Tavegia

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