Exporting IR without HPF/LPF phase shifts

[xandde1]

Hi all,

I searched the forum before posting but couldn't quite find the answer I'm looking for (perhaps I'm using the wrong search terms).

I am using the Trace Arithmetic (A / B) function to export the resulting curve as an Impulse Response (.wav) to use in a convolution reverb plugin.

However, exporting the curve as IR introduces phase shifts at the extreme lows and highs, effectively acting as an unwanted High-Pass Filter (HPF) and Low-Pass Filter (LPF) in the phase response.

I'd like to exporte the pure IR without these band-limiting HPF/LPF phase alterations. Is there a way to export the exact Impulse Response as a WAV file without REW applying HPF/LPF?

Any guidance on the correct workflow for this would be greatly appreciated!

 

[John Mulcahy]

REW doesn't apply any filters to the export. If you are exporting the windowed response perhaps you are seeing the effect of your windows, but without any data to look at there's not much anyone can help with.

 

[xandde1]

REW doesn't apply any filters to the export. If you are exporting the windowed response perhaps you are seeing the effect of your windows, but without any data to look at there's not much anyone can help with.

Hi John! Thanks for replying. I'll describe the process I'm following and attach the measurement files.

I'm trying to generate an IR between two different measurements (A over B using Trace Arithmetic).

So, the first thing I did was to capture each measurement of the sweep from 20Hz to 20kHz.

After taking the two different measurements, I aligned the SPLs and used the Trace Arithmetic of A/B. This creates a new measurement tab.

Then, I clicked on File -> Export -> Export Impulse Response as WAV and selected the A over B curve with the following settings:

• Format 32-bit Float
• Mono
• Export min phase version of IR
• Place t=0 at sample index: zero
• Export this sample count: 8k
• Sample rate: 48kHz (native rate)
• Normalise samples to peak value OFF
• Apply IR Window before Export OFF

Since both measurements were captured with the same sweep, I was expecting the extremes to look flat (a straight line over zero dB). However, when I load the IR in a convolution plugin and run a frequency response analyzer, there are roll-offs and phase shifts on the extremes of the graph:

Is there anything I can do to get rid of these high and low frequency roll-offs when exporting the IR?

Thank you once again!

Best regards,

Alexandre

 

[John Mulcahy]

There are several issues. Firstly, you limited the measurements to 20 Hz .. 20 kHz, so you are doing division on incomplete data. It would be better to measure with the sweep limits set to 0 Hz and half the sample rate. You should limit the maximum gain resulting from the division to reduce the impact of sharp dips in the divisor (e.g. at 56 Hz), by using regularisation in 5.31.3 or the gain limit in 5.40 (I suggest you update to the 5.40 beta build). Ideally one would measure in an environment that eliminated the reflections leading to such dips. If you upgrade to 5.40 I suggest you also set frequency limits for the division, e.g. 100 Hz and 10 kHz.