CSD/Waterfall low frequency noise prolem

elvischan917 · 17th November 2008, 06:42 AM

Hello!

I am creating a CSD/Waterfall plot program from an impulse response. I meet a problem that I see low frequency noise in the plot. For example, a 400 Hz electrical high pass filter will show so much energy below 400 Hz after the first FFT.

I heard that the low frequency data is invalid due to truncation error in the Waterfall plot of impulse reponse. But below what frequency the data will become invalid? I saw Sample Champion cut so many low frequency data in their plot on their website.

I wonder a direct formula between the window size and frequency.

Could anyone help?

sreten · 17th November 2008, 11:44 AM

Hi,

It is realated to room size and the first spurious reflection. The longer
this takes the longer can be the window and the lower it measures.
However splicing near field measurements is the usual path.

/sreten.

17th November 2008, 06:42 AM	#1
elvischan917 diyAudio Member Join Date: Nov 2006	CSD/Waterfall low frequency noise prolem Hello! I am creating a CSD/Waterfall plot program from an impulse response. I meet a problem that I see low frequency noise in the plot. For example, a 400 Hz electrical high pass filter will show so much energy below 400 Hz after the first FFT. I heard that the low frequency data is invalid due to truncation error in the Waterfall plot of impulse reponse. But below what frequency the data will become invalid? I saw Sample Champion cut so many low frequency data in their plot on their website. I wonder a direct formula between the window size and frequency. Could anyone help?

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17th November 2008, 11:44 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, It is realated to room size and the first spurious reflection. The longer this takes the longer can be the window and the lower it measures. However splicing near field measurements is the usual path. /sreten.

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