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Natural Science Forum / Physics / Acoustics / September 2004Frequency sweep rate
Hello! In standard IEC 1260, chapter 5.6 describes how to test 1/1 or 1/3 octave band filters for real-time operation. It is basically to perform a frequency sweep and then compare measured results with theoretical-calculated values. Chapter 5.6.5 says: logarithmic frequency sweep rate shall be low enough to permit reliable measurements for the filter bandwidth... What are the usual sweep times to test this, let say a sweep from 20Hz to 20000Hz. Is this in the range of 100ms, 1s, 10s...? Thank you. Best regards, Tomaz Kopac > What are the usual sweep times to test this, let say a sweep from 20Hz to > 20000Hz. Is this in the range of 100ms, 1s, 10s...? Thank you. If test CD's are anything to go by, then a 20Hz - 20KHz sweep is usually done in 10 seconds. Chris W  SignatureThe voice of ignorance speaks loud and long, but the words of the wise are quiet and few. -- > In standard IEC 1260, chapter 5.6 describes how to test 1/1 or 1/3 octave > band filters for real-time operation. It is basically to perform a frequency [quoted text clipped - 3 lines] > What are the usual sweep times to test this, let say a sweep from 20Hz to > 20000Hz. Is this in the range of 100ms, 1s, 10s...? Thank you. Sweep rate interacts with filter response time, and that also depends on filter bandwidth. Then there may also be a post detection smoothing filter as well, typically designated as "fast" (about 1/4 to 1/10 second) and "slow" (up to one second. For 1/3 octave filters, at 100 Hz, for instance, the bandwidth is about 20 Hz (estimated as being from there to the lower adjacent filter, i.e. 80 Hz). At 10 Hz is is, of course, 2 Hz. At 1 kHz, about 200 Hz. The response time is usually taken as the reciprocal, so 100(20) becomes o.05 seconds, etc. Sweep rates should be that this frequency increment (i.e., 20Hz when testing the 100 Hz filter) should take much longer than this response time. Ten times it (i.e. 20 Hz in 1/2 second for the 100 filter) is usually quite sufficient. Lower frequency filters are of course much slower. Angelo Campanella |
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