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Difference between revisions of "NVGate Octave Analyzer"
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→Structure and Operation
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===Structure and Operation=== | ===Structure and Operation=== | ||
The figure below shows the block diagram of the analyzer (for one channel) with octave set from 20 kHZ to 2,5kHz | The figure below shows the block diagram of the analyzer (for one channel) with octave set from 20 kHZ to 2,5kHz. | ||
[[File:octave.png|framed|none]] | [[File:octave.png|framed|none]] | ||
After amplification and antialias filtering, analog input signals are sampled at 51.2 kHz and converted by an analog to digital converter. | After amplification and antialias filtering, analog input signals are sampled at 51.2 kHz and converted by an analog to digital converter. | ||
The sample frequency depends on the value of the High Filter Setting | The sample frequency depends on the value of the High Filter Setting <br> | ||
Next, the input signals can be time weighted filters.<br> | |||
*A, B and C weight filters : These filters available in acoustic frequency range (i.e. from 20 Hz to 20 kHz) satisfy requirements from last standards IEC 651 type 0 and IEC 804 type 0. | *A, B and C weight filters : These filters available in acoustic frequency range (i.e. from 20 Hz to 20 kHz) satisfy requirements from last standards IEC 651 type 0 and IEC 804 type 0. | ||
Any other | *Any other NVGate filter need to be apply on Input Front end (real time) or Input Player (post analyisis). | ||
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After time domain filtering, the signals go to the digital 1/n<sup>th</sup> octave filter bank. | After time domain filtering, the signals go to the digital 1/n<sup>th</sup> octave filter bank. | ||
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This filter bank is based on the 6<sup>th</sup> order digital band pass. A downsampling for low central frequency filters reduces computation load. The downsampling filters have a rejection greater than 90 dB at half of each new sampling rate and a ripple less than 0.007 dB in the useful bandwidth. | This filter bank is based on the 6<sup>th</sup> order digital band pass. A downsampling for low central frequency filters reduces computation load. The downsampling filters have a rejection greater than 90 dB at half of each new sampling rate and a ripple less than 0.007 dB in the useful bandwidth. | ||
The filter range uses base 10 so that we get exact frequencies at 0.1 Hz, 1.0 Hz, 10 Hz, 100 Hz, 1 kHz and 10 kHz. | The filter range uses base 10 so that we get exact frequencies at 0.1 Hz, 1.0 Hz, 10 Hz, 100 Hz, 1 kHz and 10 kHz.<br> | ||
The following calculations are used to compute the central frequencies: | The following calculations are used to compute the central frequencies: | ||
[[File:cut off frequency.png|framed|none]] | [[File:cut off frequency.png|framed|none]]<br> | ||
Number of filter and frequency range for each filter bank: | Number of filter and frequency range for each filter bank: | ||
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* 1/1 octave filter bank: | * 1/1 octave filter bank: | ||
* can have up to 11 filters (with 1 to 1000 frequency ratio), | * Bulleted list item | ||
can have up to 11 filters (with 1 to 1000 frequency ratio), | |||
* covers range from 125 mHz to 16 kHz. | * covers range from 125 mHz to 16 kHz. | ||