ICST Ambisonics tools - Bass management

    Apr 19 2012 | 10:36 am
    Hello Everyone, this is my first post on the forum so please be patient and slap my hands if I am doing anything wrong.
    I am using the ICST tools for a music performance in Ambisonics (also trying to extend them a bit with reverberation but I will post about this in the future) and I am now facing the spectrum of bass management.
    The band plays a kind of prog jazz that involves a lot of groove and basslines so I would like to obtain the best from this.
    My previous experience was to have only one sub and feeding it with low freq and W channel only but I would really appreciate any different view in relation to the ICST tools specifically. my questions:
    - how ICST coding manage low freq? is there a crossover system already implemented?
    - if asnwer to the above is negative, how would you deliver bass to the ambisonic system? using a crossover 24 dB 4th order filter and deliver only w channel? or using a separate first order coding for a 4 sub rig distributed on a square?
    - any other ideas more than welcome.
    Forgot to say that, for the moment, I am planning to use a octagon (horizontal only rig) but this will be updated in the future if we get a bit more gigs.
    Thanks for your help.

    • Apr 19 2012 | 3:43 pm
      The ICST encoder and decders are matrix-based (operating in the same way as the matrix~ object), and don't do any particular spectral processing at all. So you'll need to deduct the low frequency content yourself. Doing so from the W signal sounds sensible.
      Cheers, Trond
    • Apr 19 2012 | 4:20 pm
      Thank you very much Trond,
      I was actually hoping to have you involved in the discussion.
      So can I use any of your tl.objects to create a crossover filter?
      Also have you ever had any experience in doing a 1st order decoding of the low freq. content? do you reckon would it make a difference?
      Thanks again
      Cheers, bassik
    • Apr 19 2012 | 11:20 pm
      Hi Bassik, You could use [cross~] to create a crossover. Check out the helpfile for details. Best, Jeff
    • Apr 20 2012 | 3:41 am
      hi, your name sounds familiar. :)
      "how would you deliver bass to the ambisonic system?"
      how does this (your) system look? ambisonics can exists just fine without any LFE.
      so i assume your target is 5.1 surround or something like that, and i would simply ignore the bass channel and use it as 5.0 or 4.0 system in order to have fun with panning.
      and in case you want to combine both worlds ... while programming i would at least not like to mix the "ambisonics" part of the patch with the 5.1 output management, that causes too much confusion.
    • Apr 20 2012 | 6:13 am
      "how would you deliver bass to the ambisonic system? using a crossover 24 dB 4th order filter and deliver only w channel? or using a separate first order coding for a 4 sub rig distributed on a square?"
      I know nothing about the ICST tools.
      First, consider whether you need a sub-woofer at all. Obviously, this depends on the bass handling of your main speakers. Also, in Ambisonics all speakers cooperate to produce a soundfield so, in general, the burden of producing bass is shared by more speakers. (While the speakers on the left pull, those on the right push.) Hence, there is less need for a sub, but your mileage may vary. Finally, if you mix bass stuff to only the W-channel then this is reproduced by all speakers, which will further reduce the burden. Try things with no sub and see.
      If you use one sub-woofer then feeding it from the W-channel is correct. What filtering you use depends on the frequency responses of your sub and main speakers. This is no different for Ambisonics than for stereo, 5.1, etc. Note that many subs include their own filtering.
      As you are using Ambisonics for music performance, I assume you are doing so in rooms a lot larger than a living room. Such rooms will be able to support localization at much lower frequencies than a typical living room, so using more than one sub-woofer should be beneficial. This is because large rooms suffer less from standing waves, and it is these that screw-up the localization of very low frequencies.
      For a horizontal-only rig you need only three subs in a triangle. This is because they operate at frequencies much lower than 700 Hz, and so can be fed from a single-band low-frequency (vector) decoder. (For your main speakers you will need four or more speakers fed from a dual-band decoder, as per normal.)
      If you ever upgrade to full-sphere, you will then need a minimum of four sub-woofers arranged in a tetrahedron.
      Can't think of anything else. If you wish to e-mail me then look on my website for the address (it is at the bottom of every page).
      Regards, Martin
    • Apr 20 2012 | 8:38 am
      Hello All,
      thank you very much for the interest in the topic and all the answer.
      It is a pleasure also to have Martin Leese in the discussion, I have used your website a lot while doing my first research in Ambisonics, thank you for sharing.
      Now back on the topic.
      Jeff - I will have a look to the cross~ object, I am not on my max computer at the moment but will share soon what I am doing
      Roman - I am actually using an 8 ch horizontal only Ambisonics rig with no plan to go to 5.1 surround. I found Ambisonics much more accurate and convincing than surround (but this can be my taste of course). I would follow the advice of delivering all freq in the speakers also as Martin suggests. (p.s. where did you hear about my name? I know yours of course form Max forum and your great insights...I am quite active also on Ableto forum for my productions).
      Martin - as said thank you for popping in. My idea (and what I have done before) was to feed the sub with the W channel only; this has happened in small rooms (usually meeting rooms) for presentation of auralisation of spaces so standing waves were of course an issue. In this particular case, the gigs will happen in large spaces (jazz clubs or medium sizes clubs) where I am expecting a minimum of acoustic treatment (apart for one venue here in London where they have sold the treatment to save the space from debts.....) so I would try to deliver the full frequency spectrum to the speakers and probably try to get an almost full range speaker system. My fear is that in many venues I will be forced to use their sub system to offer a good punch to the audience and I would not be able to arrange them as a triangle (using the in house PA system) so I would need a way to overcome this issue, so I will feed them with the W channel signal low freq content. Thank you for offering me your help, I will definitely email you for advice when I have done some test and I would need some help.
      Again thank you very much for sharing your ideas with me.
      I will post an initial patch as soon as it is in a good state; please be patient with me as I am new to Max and still learning day by day.
      Speak to you soon