## PSN-L Email List Message

**
Subject: LP filters, A/D bits and SPS**

From: "David Saum" DSaum@............

Date: Fri, 12 Jan 2001 12:06:56 -0500

I am confused about the relationships between
seismic LP filtering, A/D and SPS.
Suppose I have an 8 pole bessel filter
with a -3 db point of 10 Hz and a 16 bit A/D.
Log10(2^16)=4.81, so in power that is 96 db
dynamic range.
My 8 pole bessel response is down 96 db
at about 80 Hz.
So I should sample at a minimum of 160 Hz to
avoid aliasing that will screw up my lowest bit ?
Similarly, for a LP of 1 Hz I should sample at
a minimum of 16 SPS?
This seems to be a lot higher SPS than most folks
are using. Can we assume the seismic spectra
naturally falls off at higher frequencies so that we
do not have to depend on our LP filter
at higher frequencies?
Or is my math screwy?
Confused,
Dave Saum
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