I have a precise way to insure that when I create a new IR by mixing multiple IRs by ear on a DAW, that the result I obtain sounds exactly the same on my AXE as it does on my workstation. It takes more time than using IRMixer, but it allows you to hear and adjust your tone in real-time. This isn't new but it addresses an issue that I have yet to see addressed concerning the length of the IRs. This post is a solution to what I perceive as a problem when using a DAW to mix your new cabinet tones from IRs you have purchased. The method also supports formula sharing of the Redwirez IRs using IRMixer.
I use Sonar 8 to process my sound through several IR convolution plugins simultaneously so that I can adjust their relative levels on the fly while playing. I set the input source on each IR plugin to the amp module output (with no cab) coming from the AXE. There is a separate track in Sonar for each IR used in the mix. Once I adjust the levels of the different IR cab sims using the track faders and everything is to my liking it's time to create the new IR.
There are two ways I do this. The easy way is to mix the IRs that I used at the same relative levels as their associated tracks. If the tracks were -5, -10, and -15 dB then I mix the IRs at -5, -10, and -15 dB and normalize the result.
Another method I use is one of the free (Voxengo) deconvolver programs that use a tone sweep to get the transfer function to create the new IR. I just drag a copy of the tone sweep audio clip to all of the active tracks and record the mix to a destination track. That's then exported as an audio file and processed through the Voxengo program to yield a brand new IR. The advantage to the second method is that you can use other non-time domain (under 20ms) effects like EQ to tweak your tone before generating the new IR. The disadvantage is that it's not possible to create a "formula" mix for IRMixer to share with others.
I'll be using the first approach and abandoning using any other effects so that I can share my results in the form of formulas that can be used with the redwirez IRMixer.
There are plenty of people who do it this way or a variation on this approach, but for AXE-FX owners, in order for this to work and have the results sound the same on the AXE as they do on a DAW, you will need to truncate any samples that exceed 20ms in length. If you don't truncate all of the IRs that you use to create your new IR
prior to dialing in your tone on a DAW, the result will not sound the same on your AXE as it did on your computer workstation. It will probably sound very close in most cases unless the ambient mics are used, but it won't sound exactly the same if any of the IRs you used exceeded 20ms in length. Some will say I'm being picky here and that it's not necessary to do this. I disagree. I disagree because I can hear a difference, and with a little preparation up front I can ensure that my results are captured
perfectly, not almost perfectly, or pretty close. I see no point in spending a lot of time (which I intend to) creating good cabinet simulations using my ears if what I create is altered in the process of transferring it to the AXE.
Here’s a program (free) and batch file I "wrote" for it (the batch file, not the program) you can use to truncate your IRs to 1024 points for use in your DAW so that when you create a new IR, it sounds the same when you import it into the AXE-FX as it did when you created it on your work station.
http://sox.sourceforge.net/
Download the program from the above link called SOX and unzip it.
Paste the following code into notepad and save it as truncate.txt. Rename the extension from txt to bat so it becomes truncate.bat
rem The converted files end up in a folder called `truncated'
cd %~dp0
mkdir truncated
FOR %%A IN (%*) DO sox %%A "truncated/%%~nxA" trim 0s 1024s
Pause
Put the truncate.bat file in the same directory as the sox.exe program.
Open a second instance of windows explorer and navigate to the folder where the files you wish to truncate are stored. Select the IR files you want to truncate, and drag them onto the filename truncate.bat (sounds strange but it works). You can drag and process about 10 files at a time. I did them in lots of 9 which are how most of the Redwirez samples are organized. It took me about an hour and a half to truncate about 500 IRs.
Dragging and dropping will process the files and put them in a directory called "truncated". The unprocessed source files will remain untouched.
It's a very cool little program with a lot of other powerful utilities. Have fun!
Stephen Cole