The VQC (or SGA as it is now called) is a powerful tool, but like a lot of things from Sercel it has it's quirks. They say the devil is in the details, and this is one that hurts Sercel's otherwise very professional image.
Radio Sims, VQC and Testif-i
It is not unusual for the client rep to request that Radio Sims be recorded to disk and given to him on a regular basis. A lot of client reps use Testif-i to analyse sims and tests.
A problem arises though when saving a file to disk from the VQC/SGA environment that can prevent the Testif-i program from reading the file correctly.
What happens is that when the file is saved to disk, it is saved with a mix of the current PRODUCTION header and what the VQC has acquired, which may not match what has actually been recorded, or what is desired.
For example -
Say the crew is a 3D crew recording 4000 channels,
12 second sweep, 5 second listen time, 2mS SR.
They set up the VQC/SGA to pull 3 traces for radio sims
- Radio Ref
- Radio Return, usually the Ground force signal
When this is saved to a disk file during production, it will be saved with a header that says there are 4000 channels in the file, and 17 seconds of data.
When presented to Testif-i, it will try to read 3997 traces that are not there and will choke.
Even if it does manage to read the file, it will see 5 seconds of noise after the sweep, which can confuse some of the less knowlegeable reps.
The solution is to modify the header to report the correct number of traces in the file (3 in this case) and set the channel set end time to 12 seconds.
Remember that the times are specifed in samples, so 12 seconds at 2mS SR is 6000 (1770H) in the file, not 12000.
Here is a simple example as outline above
- The Channel set end times are changed to 6000
- The number of Aux traces is changed to 3
- The number of channels in Ch Set 2 is set to zero
- The number of live seis is set to zero
With the hex editor program change the following data bytes:
All values are in Hex.
Offset From To
64 21 17
65 34 70
69 06 03
84 21 17
85 34 70
88 37 00
89 20 00
27A 0E 00
27B 88 00
Be careful if using more than 2 channel sets - IE with tapered gains etc. If this is the case then you should set the end times and number of channels for the extra channel sets too.
The Sercel manual '408User2' has a very good description of the SEGD format as implemented by Sercel. Have a look at it to better understand what is happening.