|Nominal Response Library|
Below is some configuration-specific information to help you locate your instrument response.
Two version of FIR filters were used by the Q680 series digital signal processor (DSP). The first (tagged 900616 after the firmware version released February 1990) had non-normalized FIR coefficients. Each stage's gain varied slightly from 1, though the gain of the cascade as a whole was unity. The second version (tagged and released 920812N) had normalized FIR filters. The LOG channel notes the firmware version in use at the time of recording.
Typically, decimation for sample rates 1 Hz and higher took place in the Q680's digital signal processor (DSP). Subsequent decimation to 0.1 and 0.01 Hz streams took place in the datalogger's M680x0 processor. The fir filter that decimated 1 Hz to 0.1 Hz has a gain factor of 4.
A know exception to the typical cascade was used in the GSN network. GSN responses for sample rates from 20 to 80 Hz are identical, but for slower sample rates the cascades differ. Responses for GSN channels sampled at 1 Hz or lower are listed in the last section.
Under the original Ultrashear system software, Q680 systems corrected data time stamps for standard FIR filter delays, but did not include a small delay associated with data buffering. Q680 systems running the newer Multishear software had time stamps that were corrected for both delays.
The responses given here describe Multishear data in that the "Estimated Delay" (Blockette 57, field 7) represents the delay related to the FIR filters and the "Correction applied" (Blockette 57, field 8) is the delay due to the FIR filters and additional buffering effects. To modify these responses for Ultrashear data, set the B057F07 "Estimated delay" to the B057F8 "Correction applied" value. (Both fields should have the same value.)
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Final Sample Rate
FIR Cascade Type