What is an Impulse Response (IR) File?

An Impulse Response File is a way to create an audio snapshot of any environment: a room, an acoustic guitar body, or a guitar or bass cabinet typically in a wave file format or some other proprietary software format. Software or hardware players of this type of file use the information from the IR file to create the audio illusion of reality of you playing in that environment.

How do you make an Impulse Response (IR) File?

You play through a speaker either a sweep of frequencies, pink noise, white noise, or some have done it with a balloon pop in the space. You record the sound in that environment. Then you use some software to mathematically remove the sweep of frequencies, pink noise, white noise from that recording. The resulting recording file captures the acoustical sound properties of that environment along with the coloration of the microphone and mic preamp used to record it (this is the IR file).

How do you use an Impulse Response (IR) File?

You may use other hardware guitar amp modellers, IR based reverb units, or a dedicated guitar cabinet emulators, or software to process your audio or what instrument you are playing using these IR files. Using these files with the hardware or software give the illusion that your audio or your playing was created in that environment or played through that speaker cabinet. The maker of the hardware or software will have detailed instructions of how to load these IR files to use them.

Which format of Impulse Response (IR) File is good to use with the software or hardware I have?

The manufacturer of the software or hardware will tell you the sampling rate frequency (labelled in KHz), bit depth (usually 16, 24 or 32 bits), and length of file it will accept as valid. Most software and hardware have ways of trimming the IR file if it is too long, but the file you need to select needs to agree with the sampling rate and bit depth specs in order to avoid strange results or errors. My files work with most manufacturers' products if you compare specs. If the manufacturer has a proprietary format, they usually also provide a software to convert & trim the wav files I provide into that format.

My particular hardware lists something called samples or points in my required specs for an IR file. How do I know which of your IR files to use with my hardware?

Some manufacturers deal in samples or points rather the specs I discussed above. Here is the formula you can use to calculate the samples or points to find the nearest length file to use:




Number of milliseconds X Sample Rate in KHz = Number of Samples in Total

For example: 200 ms X 44.1 KHz = 8,820 sample points

Why should I use an Impulse Response (IR) File to emulate a Guitar Cabinet or Bass Cabinet?

Owning and transporting Guitar or Bass Cabinets can be expensive, back breaking work, take up space in your home or onstage, and need to be played at volume levels that may not be agreeeable to spouses, pets, roomates, bandmates, and/or neighbors. An IR file used with software or hardware allows your get to that high volume reality without the social, financial, human rights, and spacial pitfalls. You can use 10, 20, or 30 cabinets easily as IR files and they will most likely fit in your hardware or software, as well as allow for you to actually have room in your home or fit other people on stage. You can get those cabinet sounds using IR files and not deafen yourself or others with monitoring levels. Also, because the miking of the cabinet is already built into the IR files, you will always have your sound and not be at the mercy of the skills of a soundman, or need to travel with or own expensive microphones to get your sound.

Why should I use a Speaker Cabinet Impulse Response (IR) File if I record or play live using a mic preamp or direct box?

Impulse Response (IR) Files are just another color in your tonal palette for shaping your sound. Using a mic preamp or direct box to get your sound is perfectly OK or acceptable. Many players use that technique to get their sound. However many players also use amps and cabinets to get their sound. If you want to create your sound using amps and cabinets, then using amp modellers with Impulse Response (IR) Files will get you to that reality of sound in a much more cost effective, manageable, & portable manner.

If a speaker cabinet acts like an EQ to shape the sound of an amp, why not just use an EQ to do this tone shaping rather than use Impulse Response (IR) Files?

A speaker cabinet is more than a EQ. The speaker cabinet adds resistance to the amp which changes the sound and also has changes the timbre of the sound with the way the baffles or ports in a cabinet and the speaker cone materials resonate. A properly recorded Impulse Response (IR) File gives you not only the frequency response of the cabinet but also captures the timbre of the speaker cabinet as it resonates with all those frequencies to give you the realistic sound as if you were physically playing a miked up version of the cabinet. EQ with enough selectable boosts and cuts can in theory simulate the frequency response, but EQ alone cannot replicate the timbre of the cabinet or unusual speaker cone materials, such as aluminum speaker cones for example, can bring to a sound. So if your amp modeller allows you to adjust the power amp resistance to simulate being hooked up to that cabinet, a good Impulse Response (IR) File will give you the rest of the audio picture of playing using that miked up cabinet.

What advantage will using a guitar or bass amp modeller with Impulse Response (IR) Files give me when recording my music?

Once you have your sound dialed in, you will be able to record and make much more efficient use of your time thinking of musical ideas or performing rather than worrying about if the mic is in the right position on a cabinet or that somebody sneezed in the room where you are recording. You will get a more consistent tone from recording session to recording session too with minimal setup time. Using this technology also opens you up to the possibilities of recording a dry guitar amp and virtually re-amping it at a later date to shape the sound better to fit the final recorded arrangement of the song.

What advantage will using a guitar or bass amp modeller with Impulse Response (IR) Files give me when playing music live?

If you don't have a team of roadies following you around, then using an amp modeller with Impulse Response (IR) Files will allow you to have a transportable guitar or bass rig that sounds kick ass but will not break your back or fatigue you from moving heavy cabinets around before you even play a single note. You will also be be able to play with cabinets that might not be economically feasible to own in your part of the world for a fraction of the cost to physically own the cabinets. You will be able to recreate your favorite players' sounds much more easily if you select the correct Impulse Response (IR) Files that correspond with their setup. If you do have a team of roadies, then using an amp modeller with Impulse Response (IR) Files will allow you to save money on carting and transport costs, help you avoid customs hassles transporting massive amounts of gear from country to country or using local backline equipment that may not be in the best shape, save on setup, soundcheck, & breakdown times, and give you a consistency of sound from gig to gig.

Why don't you give details anywhere about the environment you use to record?

Both the physical recording space, the software setups, reference power amps, and microphone recording techniques I use are all considered proprietary trade secrets and I will not disclose them no matter how much people beg. If you like the results of the samples and trust what people have said about my past cabinet Impulse Response (IR) Files, then you should be able to buy my files with the ultimate confidence.

Why don't you give out free samples?

Free samples would allow unscrupulous people not bound by the user agreement to reverse engineer the files or attempt to steal or redistribute them without my consent. There are many people that distribute free Impulse Response (IR) Files, but I am not one of them. I incur considerable expenses constructing my recording space, building up & maintaining my mic collection, purchasing hardware & software, maintaining a website, and renting many of the cabinets I offer for sale in file form, in addition to the 100 to 200 hours of my time that it takes to produce each of these Cabinet Impulse Response (IR) File packs. If I invest time and money to bring you something of value, then I think it's only fair that I receive a fair amount in return for that something of value.

Why do you sell a Fractal Audio Systems version and a Wav version of the same cabinet?

Fractal Audio has a very specific licensing agreement that disallows me to sell WAV versions of the same files I produce in their proprietary formats, which makes sense if you think about it from their point of view. The Fractal version also includes bundled presets that include interesting amp/cabinet pairings that would be useful if you own an FAS product, but useless if you use another modelling platform. The WAV files therefore are a different version to honor that agreement

In the Fractal Audio Systems version cab packs, why don't you offer the .ir files anymore and only offer .syx files?

Fractal Audio Systems considers such an offer as a violation of their licensing agreement. If you need more than ".syx" files, you are going to need to purchase the WAV pack and convert the files yourself in order to mix in Cab Lab3 by using the "WAV2SYX" tool contained within it. The process really isn't complicated and takes 5 minutes to do on a decent computer. I tried to make the case for you users regarding including the .ir files in addition to the .syx files in the Fractal pack, but Fractal Audio Systems was very convincing in enforcing this point of the licensing agreement.

Why do all commercial Impulse Response (IR) File providers have nicknames for the manufacturers/brands of the guitar or bass cabinets that they recorded to create the files?

Most cabinet manufacturers do not care if you record their cabinets, however they do legally defend unauthorized commercial use of their company and brand names. Therefore under fair use law, we can come up with a nickname and say the the nicknamed cabinet is based on Manufacturer X's cabinet or is in tribute to it, but we cannot outright name our files by the original manufacturer X's naming without being subject to a lawsuit. Purchasing the legal naming rights for file use would be so cost prohibitive as to make the files unaffordable.

Why does the lineup of microphones change slightly from one Cabinet Impulse Response (IR) Files Pack to another that you offer?

Not all mics particularly work well on certain cabinets. I have broad musical interests that run from lo-fi to hi-fi, from punk to jazz, to country, to rock, to Broadway, to the truly avant-garde. If I cannot think of a context in any of those environments where the sounds of that mic on that cabinet work, then I make the editorial decision to not include that mic or certain positions of that mic on that cabinet in that collection. I want to give you IR files that you can work with easily, maybe roll off a little low end or high end if you need to, and you are ready to play.

Why don't you EQ your Impulse Response (IR) Files so that I don't have to do any work?

Unfortunately, I do not have your hands, your exact instrument setup to your desires, your playing style, your exact monitoring system in your room with your ears, nor can I predict the music you are going to play with these IR files, nor can I guess what the instrument arrangement will be. If I took frequencies away and you actually needed them to be there, you would possibly dismiss the files as useless or junk. That small investment of your time in shaping your tone will pay off handsomely if you are patient.

If I have a 7 or 8 string guitar, Chapman Stick, or Warr Guitar, should I use your bass cabinet or guitar cabinet Impulse Response (IR) Files?

There are no rules!!! Some 6 string guitar players even like to play using my bass cabinet Impulse Response (IR) Files. Some bass players have been known to use guitar IR files. Since there is no physical harm that can come to virtual voice coils or speaker cones represented as ones and zeros, your possibilities are endless! Experiment and have fun!!!


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