VI to calculate time decay of acoustic signal?
im using a b&k8104 transducer to transmit a 75KHz signal sampled at 2MHz generating 100000 samples and receiving it using a neptune d70 receiver in an underwater tank. i need to calculate the reverbration time (i.e. the time taken by the signal to decay by 60 db) but i'm unable to see the time domain plot clearly in labview. its riddled with noise. maybe my vi is faulty. can anyone help me if they've made VIs that calculate such time decays?
P.S. I'm unable to attach my vi here as this is a diferent computer.. but its a simple vi where i simulate a signal and take its output through DAC. Then receive the input through another DAC and see its time domain plot and FFT.
PLEASE HELP!
I assume (but you didn't say) that you present a brief 75KHz "chirp", rather than playing it continuously while taking the 100000 samples. If so, then divide the post-chirp time into bins perhaps similar to the chirp length and take the FFT of each set of bins. For example, if your chirp was 2 msec long, take the FFT of 0-2, 2-4, 4-6, 6-8, msec intervals and look at the power at 75KHz (your signal). Find the time at which the signal has fallen by 60dB. You basically don't need the time-domain signal to do this.
Disclaimer -- I've never tried to do this, and have no expertise in acoustics. This just seems to be a logical thing to try ...
Bob Schor
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Edited by: UserMB on Jan 11, 2012 5:14 PMOne way...
ME_XE?with t as
2 (
3 select 'ORACLE' col1, 'A' col2, to_date('1/01/2012', 'dd/mm/yyyy') col3
4 from dual
5 union all
6 select 'ORACLE', 'A', to_date('2/01/2012', 'dd/mm/yyyy')
7 from dual
8 union all
9 select 'ORACLE', 'B', to_date('3/01/2012', 'dd/mm/yyyy')
10 from dual
11 union all
12 select 'ORACLE', 'C', to_date('4/01/2012', 'dd/mm/yyyy')
13 from dual
14 union all
15 select 'IBM', 'A', to_date('1/01/2012', 'dd/mm/yyyy')
16 from dual
17 union all
18 select 'IBM', 'A', to_date('2/01/2012', 'dd/mm/yyyy')
19 from dual
20 union all
21 select 'IBM', 'A', to_date('3/01/2012', 'dd/mm/yyyy')
22 from dual
23 union all
24 select 'IBM', 'A', to_date('4/01/2012', 'dd/mm/yyyy') from dual
25 )
26 select
27 col1, col2, min(col3), case when max(col3) = max_company_date then to_date('31/12/2999','dd/mm/yyyy') else max(col3) end
28 from
29 (
30 select col1, col2, col3, max(col3) over (partition by col1) as max_company_date
31 from t
32 )
33 group by col1, col2, max_company_date;
COL1 COL MIN(COL3) CASEWHENMAX(COL3)=MAX_COMP
ORACLE B 03-JAN-2012 12 00:00 03-JAN-2012 12 00:00
ORACLE A 01-JAN-2012 12 00:00 02-JAN-2012 12 00:00
ORACLE C 04-JAN-2012 12 00:00 31-DEC-2999 12 00:00
IBM A 01-JAN-2012 12 00:00 31-DEC-2999 12 00:00
4 rows selected.
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