WEINSTEIN: EXPLOSIVE SOUND-SOURCE STANDARDS 



It is illustrative to compare data processing results of dif- 

 ferent facilities. Each facility used a different duplicate of the 

 original recording, either direct or FM, depending upon available 

 equipment. Figure 13 compares about 100 shots for Systems (1) and 

 (2) . System (1) is fully digitized using FFT processing. System (2) 

 uses analog 1/3-octave filters followed by digital processing. The 

 comparison is for the 50-Hz band only, for three different hydro- 

 phones. Independent processing yielded biases from + 1.47 dB to 

 + 2.13 dB, and standard deviations from 1.28 dB to 2.06 dB. One of 

 the problems identified at this time was that the two facilities 

 made independent and different determinations of signal duration. 

 When these were made consistent and the data reprocessed, the bias 

 was reduced to between + 0.95 and + 1.85 dB, and the standard 

 deviation to between 1.05 and 1.52 dB. 



To help identify the reasons for the observed differences, the 

 tape recording used on System (2) was then processed with System (1) . 

 The additional improvement was a few tenths of a decibel, identify- 

 ing the major source of the differences shown as resulting from 

 differences in the processing systems. 



A comparison between System (1) and another hybrid analog- 

 digital system (System (3)) is shown in Figure 14. The agreement 

 is somewhat better. These results, combined with the prior compari- 

 son of analog and FFT processing, with all else the same, suggest 

 that the differences seen in the previous figure are not totally 

 attributable to differences between analog and digital processing. 



Figure 15 compares System (1) and a totally analog shot 

 processor. System (4). It employs 1/4-octave rather than 1/3-octave 

 filters. A simple 10-log bandwidth ratio correction was made. 



81 



