Has anyone cracked open an IR to see what all its really doing?

Discussion in 'Digital & Modeling Gear' started by aldridt11, Apr 9, 2019.

  1. aldridt11

    aldridt11 Member

    Messages:
    250
    Joined:
    Jan 11, 2018
    Obviously most players agree that IRs are a big part of what has been missing in capturing real guitar sounds.

    I know that it is the mic(s) plus the mic placement, the cabinet, etc. etc.

    But what is the IR using to capture this information? It is just EQ? Do they use compression, also? Is there something else?

    I do not intend to try to bypass using IRs with this information.

    I'm just curious.
     
  2. phil_m

    phil_m Supporting Member

    Messages:
    10,020
    Joined:
    Jun 29, 2012
    Location:
    East of the Sun, West of the Moon
    I've cracked many an IR open to feast on the goo inside...
     
    spiral, G34RSLU7, Jdstrat and 6 others like this.
  3. metropolis_4

    metropolis_4 Member

    Messages:
    3,589
    Joined:
    Dec 14, 2010
    Here you go, one cracked open IR:

     
  4. stickyFingerz

    stickyFingerz Supporting Member

    Messages:
    2,148
    Joined:
    Jan 7, 2017
    An IR file doesn't contain software code - it's a digital representation of an object's response to a sharp impulse (e.g. a room's reverb or a speaker + cabinet output).

    As such, it isn't doing anything. It's a collection of data points for the IR engine.
     
    Last edited: Apr 9, 2019
    MikeMcK and yeky83 like this.
  5. Watt McCo

    Watt McCo Member

    Messages:
    8,142
    Joined:
    Oct 1, 2016
    https://en.wikipedia.org/wiki/Finite_impulse_response

    No compression. Like an EQ, but not "just EQ" because no EQ can be as resolved as the IRs commonly used for cabinet emulation.
     
  6. stickyFingerz

    stickyFingerz Supporting Member

    Messages:
    2,148
    Joined:
    Jan 7, 2017
  7. Frank Ritchotte

    Frank Ritchotte Silver Supporting Member

    Messages:
    5,556
    Joined:
    Oct 12, 2015
    Location:
    Calabasas, CA
    It’s unicorn blood. Just don’t touch it.
     
  8. aldridt11

    aldridt11 Member

    Messages:
    250
    Joined:
    Jan 11, 2018
    Ok, convolution reverb....I had never heard of it.

    Some of this is over my head, though.
     
  9. cliffc8488

    cliffc8488 Member

    Messages:
    1,058
    Joined:
    May 13, 2006
    It's analogous to a sampler. Consider the sample of, say, a kick drum. You make a short recording of that and then "trigger" that recording. If you want the kick drum louder you make the trigger louder.

    Now assume you trigger that recording thousands of times a second at varying amplitudes. That's essentially how IRs and convolution work. You trigger the recording at the sample rate and each playback is weighted by the sample amplitude.
     
    banyun3b, Ferg Deluxe, ejecta and 3 others like this.
  10. Karl Houseknecht

    Karl Houseknecht Supporting Member

    Messages:
    3,846
    Joined:
    Nov 24, 2008
    Location:
    VA
    It will keep you alive, even if you are an inch from death, but at a terrible price. You have slain something pure and defenseless to save yourself, and you will have but a half-life, a cursed life, from the moment the blood touches your lips.
     
    SamPaoli, G34RSLU7, Madmax25 and 10 others like this.
  11. BCy2k

    BCy2k Member

    Messages:
    1,639
    Joined:
    Mar 24, 2008
    Location:
    Colorado
    Would it be fair to say it's sort of a sample of a specific configuration of audio DNA?
     
  12. cliffc8488

    cliffc8488 Member

    Messages:
    1,058
    Joined:
    May 13, 2006
    There's no such thing as "audio DNA".
     
  13. MaxTwang

    MaxTwang Member

    Messages:
    2,170
    Joined:
    Oct 15, 2007
    An impulse response is a recording of a response to an impulse. IRs are often WAV files like any other recording. It may be easier to think of IRs used for natural room reverb - the IR is a recording of the reverb itself with the sound being reverberated (impulse) removed - leaving only the response.

    To create an IR one has an impulse (sine wave, gun shot, click, etc) and a recording of that impulse through a speaker, or in a room with natural reverb, then the impulse is subtracted from the recording - leaving a recording of the 'response' to the impulse.

    If the impulse was a sine wave that was played through a speaker, then the impulse response is the recording of the sine through the speaker with the sine wave subtracted - leaving only a recording of the influence of the speaker.

    For room reverb one might use a gun shot as the impulse then record the sound of the gun shot in the room with the room's natural reverb. The resulting impulse response would be the room recording with the gun shot subtracted - leaving only a recording of the reverb of the room.

    The device/program you load IRs into apply the IR to your guitar signal resulting in an approximation of your guitar played through a specific speaker/cab/mic and/or a specific room reverb.

    The algorithms to subtract the impulse from a recording of that impulse through a speaker (deconvolution) and to apply an IR to a signal (convolution) are very complex and they affect frequency over a period of time (the length of the IR recording) - the process is 'convolving' or combining your live guitar signal with the IR recording.

    * This is an attempt at a 'simple' explanation and in no way an attempt at a dissertation on Convolution.
     
    Last edited: Apr 9, 2019
    blandified, MikeMcK, Jackeb and 6 others like this.
  14. bdrepko

    bdrepko Supporting Member

    Messages:
    1,938
    Joined:
    Aug 29, 2014
    Location:
    Gilbert, AZ
    If you open it the warranty is void.
     
    spiral, G34RSLU7, jozh and 13 others like this.
  15. Mark Al

    Mark Al Member

    Messages:
    579
    Joined:
    May 24, 2018
    One question for you guys, do you prefer IRs that contains minimum/no room information or IRs with some room information?

    The former sounds almost completely dead with no verb, while the latter may sounds a tad more natural, as a result people may mistakenly prefer the latter, but it actually colors the sound and IMHO is less ideal. With the former, one can add whatever reverb on top anyway. So dead sound IR is my preference.

    Lastly, I imagine to take a good IR with no/minimum room info, one need to acoustically treat the room extensively with absorber but no diffuser...
     
  16. BCy2k

    BCy2k Member

    Messages:
    1,639
    Joined:
    Mar 24, 2008
    Location:
    Colorado
    Right. Well I was speaking about the wav file metaphorically ... my bad
     
  17. burningyen

    burningyen Member

    Messages:
    14,023
    Joined:
    Jan 4, 2002
    Location:
    CT
    I'll use either depending on the context.
    You need a space with a smooth floor where the walls and ceiling are far enough away that reflections don't arrive at the mic before the cab response has trailed off. Lots of posts about far-field IRs and ground plane measurement here and over on the Fractal forum.
     
    yeky83 and Mark Al like this.
  18. vtgearhead

    vtgearhead Silver Supporting Member

    Messages:
    974
    Joined:
    Aug 24, 2016
    Location:
    Burlington, VT
    This has been beaten to death many times around. Please search for Jay Mitchell's highly informative posts on this exact subject. One could power a small city on the amount of half-understood and misunderstood information flying around.
     
    BCnSTL, Viabcroce, FPFL and 1 other person like this.
  19. yeky83

    yeky83 Member

    Messages:
    2,152
    Joined:
    Dec 11, 2007
  20. mbenigni

    mbenigni Member

    Messages:
    6,560
    Joined:
    Jul 6, 2015
    So... fair, but meaningless. :D
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice