IR Capture Cap White noise or Sweep?

#1

Hi,

I’m trying to capture an impulse response (IR) from my guitar cabinet. I researched different methods and found two: using white noise and a sine sweep. What are the differences? Anyway, I tried with white noise because it seems easier. I found this tutorial:

The man in the video adjusts the Pro Tools grid to samples. Can I do this in Ardour?

Thanks.

#2

Hi,

I commissioned a tool from the developer of LSP plugins a few years ago to create impulses responses using sine-sweeps. You might find that tool useful for this purpose too - GitHub - sadko4u/room-raider: Tool for performing off-line impulse response capture of the room

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#3

The advantage of white noise is that it works in noisy places (e.g. outdoors), where the use of a starter-pistol is not possible, and popping a balloon is too soft.

For capturing IRs in a controlled environment, or when cloning effects using a cables (no mic) a sweep is usually preferable.

The canonical tool on Linux is aliki (http://kokkinizita.linuxaudio.org/linuxaudio/downloads/aliki-manual.pdf).

If you like the commandline and need to capture man IRs: GitHub - x42/jack-ir: JACK Audio Batch Impulse Response Recorder
I used this tool to capture some of the IRs available at x42 Zero Config|Latency Convolver

–
PS. Ardour comes with a Lua script to capture IRs, but that is currently volatile. the IR is not saved to disk: _ircapture.lua · GitHub

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#4

Not the grid per se, but you can change the clock to samples and show a ruler…

right-click on the clock to change it to show samples. and Menu > View > Rulers
image

It’s unclear what a sample-grid would do, in Ardour the max zoom level is 1 pixel per sample. So the whole screen would be filled with grid lines :slight_smile:

#5

PS. Short of capturing your own. You can get an exhaustive collection of cabinet IRs here: http://www.osirisguitar.com/wp-content/uploads/7deadlysins%20Impulse%20Pack.zip

#6

Thank you for the responses and for the link to download the IRs. However, I would like to do it myself to experiment and understand the process. Setting aside the topic of GRID to Samples, do you know if I can select just one sample? Either way, I’ll try both methods, with white noise and sine wave.

In any case, how would you do it using the white noise method and Ardour?

#7

You cannot select a single sample in Ardour. You can create a time (range) selection that is just 1 sample long. Not sure what the purpose would be anyway - you cannot edit audio data in Ardour, ever.

#8

certainly you can, but what is the purpose of it?

Note that the selection clock (here in Ardour 8) is wrong.
Range [start, end[ (exclusive end), should show length = 1.

A single sample selection (here a delta impulse) looks like
image

#9

Thank you again for the answers. This is my first time working with IR, and I have another question. Once I apply the IR to the DI signal, should I ‘bounce’ this track, or can I add effects to it as if it were a normal track?

#10

I did a quick/dirty IR capture test: here just a (somewhat noisy) loopback using the Ardour Lua script:

  1. Calibrate I/O Latency (Menu > Window > Audio/MIDI Setup)
  2. Create a mono track - this will be used to record the IR.
  3. Disconnect the input and output of that track.
  4. Add a mono bus and load the IR Capture plugin on the bus.
  5. Connect the left output of the bus to the mono track’s input.
    The deconvolved Impulse Response will be output on that channel.
  6. Connect the right output of the bus to a hardware playback port, matching the system you want to capture.
    A sine-sweep will be played on that channel.
  7. Connect the bus’ input to the return signal (hardware capture) of the system under test.
  8. Record Arm the track (from 2)
  9. Record Arm the session
  10. Open the GUI of the IR Capture plugin, enable “Capture”
  11. Roll the transport.
  12. Wait 10 sec (recording stops automatically).
  13. Select the region on the mono track: Region > Edit > Strip Silence and/or manually tweak the region start:
    move it close to the initial impulse.
  14. Region > Gain > Normalize, or manually adjust gain.
  15. Disable region-fades of the region: Region > Fades
  16. Export the region to save the IR file (Region > Export)

I then loaded that IR file into a convolver and checked the response. Which is supposed to be flat until 20kHz. Here it is close, good enough for a first take. - Note that due the slight pre-delay (impulse in the IR is not at 0), the analyzer shows phase issue.

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#11

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