Simulated IR made with Goldwave

This post is just for crazy knob tweakers like myself. To me, the Kemper is a science lab that I play in all day long creating crazy inventions.

Disclaimer:

I am a big fan of Goldwave. A stand alone audio editor that has been around for years. Recently I started using an effect called the Spectrum Filter. This effect uses FFT and allows you to draw the frequency response you would like. Goldwave can usually be used in demo mode because the author is a god. I use it everyday for so many things. I am not affiliated in anyway to the company/author. These methods can be used in any audio editor.

LETS DO IT:

Step 1 is to get a base Impulse audio file. You can make one in Goldwave by manually editing a single sample in a file or use something you already have (made or from web, etc). In theory a single sample is a very short square wave signal. Since the rise of the wave is instant, it will create/include all of the odd harmonics after it. So all of the audio frequency spectrum will be present in this tiny pulse.

Step 2 is to open the Spectrum Filter in Goldwave. From this dialog you can add/remove points on a frequency plot to create the response you are going for. Once you apply this effect to the Impulse file you should get a response very close to the curve you drew. Looking at the resulting waveform you can see it is no longer a square wave.

Step 3 is to apply some gain to the signal to get the most volume out of the final IR. In Goldwave you can choose the Maximize Volume effect. I usually set the new volume to be -3dB. This gets me close to the normal Kemper volumes and makes it easier when comparing IR/CAB so the volume is not jumping around.

Step 4 is to save the file. You can select many different formats in the dialog. IRs are simply WAV files. I use the standard CD quality values of 44.1 kHz sample rate, mono, 16 bit.

Step 5 How you get this into the Kemper is up to you. I have a folder in Rig Manager that I drag them into so I can sample them and rebuild then over and over the get the right response I am looking for.

THE END

As of late, I have been focusing on making DI profiles and then designing these custom IRs to fit. The results have been pretty good.

I recently added a profile to the exchange of just a Metal Zone pedal and one of these IRs. No amp, speakers, or microphones we hurt in the making of this profile. Just pedal and IR. And it came out pretty cool. Way better than I imagined it could.

IMPULSE FILE

I could not attach a WAV file here. So I do not have an easy button for you. Generically, common IRs are based on 1024 or 2048 samples. Using a sample rate of 44.1 kHz means we need approx 46mS of audio. You will want some dead time before the pulse, so I used 50Ms. I created the IR pulse at around .45mS.

Quote from DonPetersen

this sound can also be achieved by the 'Character' parameter in the CABINET module:

I read the CHARACTER effect as increasing or smoothing peaks in the frequency response. You still need a response to begin with. That is where this post comes in. Creating a custom IR (freq resp).

The example I posted above was a from a graph I found on the web of a V30 speaker. I think the graph was created from a speaker in air (not in a cabinet) because the low end response is very low. There are no large peaks or dips in the response. In my mind, large peaks and dips (errors in the response) would be from cabinet resonances and microphone placement issues. That is why I wanted to try this method out. To get the desired freq response without the hassle of fighting mic positioning, cab resonance, EQ coloring, etc.

It is an attempt to get a more realistic response of what you would hear at the cabinet if the cabinet was very flat and you had perfect microphones , EQ, and placement. You could add more points to the curve to get resonances and suck outs if you want. I have not tried, because I am trying to do the opposite of that.

The other point is to get an IR that is EQ'd exactly how YOU would want it. Everyone has different tastes. And the Kemper only has 4 possible FX slots after the amp. So, tweaking the IR could free up a slot after the amp that would possibly be taken up by an EQ FX. I hear people on the forum always asking for more slots. This is one way you could free up a slot. But it will take some work and is not super easy. But it is incredibly fun for some of us.

I hear a lot of great tones on the Rig Exchange that are ruined by poor mic placements. There are large frequency suckouts here and there that make it sound like it is in a tunnel. This totally ruins the sound for me.

So you have three options:

- Adjust the Character as mentioned. This cant fix large problems. It can't add in the missing frequencies without modifying the overall response. So it is great for small changes, but not large suckouts/peaks.
- Use a different CAB/IR. Easiest fix. But every IR has its own sound. So you have to sort thru a lot to get the perfect tone.

- Build your own IR. You can use the method I outlined for greater control. Or use a tone matching program to basically do the same thing using some prerecorded material to create the freq resp for you.

I am not an expert in this field. I am just a guy who likes to spin the knobs and create some fun new things. And to me the Kemper is the most amazing device ever created for guitar. It allows us to have complete control of all aspects of a profile.

Quote from DonPetersen

Using a few bands of EQ doesn't really give you a whole lot of control, there are tools to create a IR by hand.

When you design the frequency curve in Goldwave, you do it using points. You can add/subtract points. I have not hit a limit on the number of points yet. For testing purposes I added 75 points and got tired of clicking

So you can draw any crazy curve you want.

The point was to show how easy it can be. There are probably lots of tools out there as you suggested. This is just one.

Quote from V8guitar

Seriously, love the idea of how you are creating your own starting points and working with the Kemper on potentially unique sounds.

This is the whole point of the stuff I normally do on the Kemper. There are 1000's of great amp captures on the exchange. Why not try to give users some different options. I think you even said today, I may not use some of the extra features on the Kemper, but I want them.

To expand on making an IR:

The 1st step for this demo was to get the frequency response curve of a normal guitar speaker. Next I selected some frequencies where I felt the freq curve was changing. Then I drew this curve by clicking on the selected points of interest in the Goldwave Spectrum Filter graph area.

Now that I have the base response, I can tweak the tone by changing or adding points. This is where this becomes a useful tool that lets you tailor the response to your sound.

NOTE: To edit a point, just click on the point and drag it. Or you can select the point in the dialog text fields area and type in exact values.

TIPS: In Goldwave, you have different audio playing options. I always make one option a repeat. Clicking this option will play the selected audio clip numerous times (I pick 100). Once I have the IR created, I play the loop and Goldwave draws the max values it saw in the FFT spectrogram window.

You could also select any isolated guitar tracks you have and play them to see what the frequency response looks like on the recording. This works best with high gain stuff because the extra harmonics (from the gain) fill out the curve better. This would basically be Tone Matching. Get a curve, then draw that curve manually in the Spectrum Filter.