Impulse Scaling

[jtalden]

Is it possible to scale an impulse within REW? The offset control and “Add Offset to Data” will shift the chart SPL value, but the impulse itself seems to remain unchanged. Saving and reopening the mdat has no effect and exporting the offset impulse into a wav file and reloading it also does not seem to help.

The attached file contains a ’0deg Mic’ impulse that has been shifted from ~83 dB to 0 dB SPL with ‘Add Offset to Data’ applied. The unnormalized impulse still shows the ’0deg Mic’ impulse size is unchanged and the A*B trace arithmetic results in about 84 dB instead of the expected 0 dB SPL level.

 

[John Mulcahy]

Generally there is no need to care about the data offsets and the trace arithmetic results should be consistent with the levels shown on the traces. The data offset for a trace arithmetic result depends on the offsets of the A and B traces, the data offset for a measurement can be seen in the Info panel. In the attached mdat the 2i2G2>Rotel@12V trace seems to be the oddity, it has a data offset of 95 dB even though the levels are around 0 dB and trace arithmetic using that measurement gives odd levels. Not sure how its offset and levels came to be inconsistent, though it is from an early 5.20 beta release so perhaps there was something iffy about the offsets in that release.

 

[jtalden]

Thanks John.
I sounds like I was focused on the wrong impulse. I will try to sort this out again.

 

[jtalden]

The problem was that I had selected a 'Soundcard' calibration result of my measurement chain (2i2G2>Rotel@12V) and used it as if it was a normal measurement. By selecting a normal measurement of the soundcard chain it now provides the expected A * B result near 0 dB, Thanks!