I want to use csound to make a computer-based active bass canceller. 
Basically I can set up a microphone, speakers, and sound card in my 
bedroom. Can someone point me to the necessary signal processing to do 
this, or is it a really simple filter of some sort?

Mike



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I've been at the max msp expo and I saw a presentation about doing this, Alex Harker's HISStools. The idea was that if you take an impulse response of the room (the recommendation was to use an exponential filter sweep) you could then use convolution with the inverse of that impulse response (mirror it over the 0 db line) to get a flat result. I suppose you could probably use that inverse impulse response to set a filter instead of using convolution, but it worked really well in the demonstrations.

I know there are good processes to use convolution in csound, but are there methods to take an impulse response?

A

Sent from my iPhone

On Oct 15, 2011, at 6:23 PM, Michael Mossey  wrote:

> I want to use csound to make a computer-based active bass canceller. Basically I can set up a microphone, speakers, and sound card in my bedroom. Can someone point me to the necessary signal processing to do this, or is it a really simple filter of some sort?
> 
> Mike
> 
> 
> 
> Send bugs reports to the Sourceforge bug tracker
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> 


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On 10/15/2011 6:23 PM, Aidan Collins wrote:
> I've been at the max msp expo and I saw a presentation about doing this, Alex Harker's HISStools. The idea was that if you take an impulse response of the room (the recommendation was to use an exponential filter sweep) you could then use convolution with the inverse of that impulse response (mirror it over the 0 db line) to get a flat result. I suppose you could probably use that inverse impulse response to set a filter instead of using convolution, but it worked really well in the demonstrations.
>
> I know there are good processes to use convolution in csound, but are there methods to take an impulse response?
>
> A
>
> Sent from my iPhone
>
> On Oct 15, 2011, at 6:23 PM, Michael Mossey  wrote:
>
We might be talking about different things.

My bedroom has some strong bass modes that are really bothersome when 
trucks drive by or my roommates play loud music. I'm talking about actively 
suppressing them using some kind of control system (with a microphone and 
speaker), the same technology that active noise-cancellation headphones 
use. I can't remember any of the control system theory we used in college.
Mike



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On 10/16/2011 11:02 PM, Josh Moore wrote:
> Noise cancellation headphones rely just as much on pressure/self noise 
> (music) generated as the noise outside of the environment....
>
> The technology you are talking about is impossible without modifications 
> to the room. You'd have to outfit something to absorb the vibrations. 
> Theoretically you could use the same technology, but outfitting a room 
> for this would be just as much work as soundproofing a room since you 
> would have to separate the outside world from the inside world.
>
> In headphones, it's pretty easy because the headphones create that 
> different space for you and all of the acoustic design can be condensed 
> in such a small space.
>

Hi Josh,
Thanks for the reply. I don't understand, though, about the isolation. 
Noise-cancellation headphones don't isolate the outside world nor do they 
absorb the noise. I thought they generated an inverse signal, maybe using 
some kind of control system, employing a small mic near the ear, and using 
a control system to make sure the signal in the mic tracks the music 
signal. If it starts to deviate, the control system alters the signal to 
the drivers. Maybe I'm wrong.

Maybe I should clarify that I'm only interested in cancelling the bass 
standing waves. In my case there's no music signal. The target signal is 
golden silence.

Mike



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On 10/21/2011 12:05 AM, Josh Moore wrote:
> If there is a truck driving outside that's generating lots of vibrations, 
> those vibrations will be everywhere because they're bouncing off lots of 
> things and in a much larger space. 

Ah, yes, but I'm only trying to nullify the *bass resonance modes*.  The 
truck noise across the spectrum will still be there, but the bass modes are 
30 db+ louder than the direct truck noise.

Mike



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if you have 2 bass bins you could set up an experiment i think. set up
one outside to generate your bass mode. set up the other inside for
cancellation.  using a constant frequency, try to dial in a phase /
delay (for a single frequency its the same effect) amplitude of the same
signal that cancels out the mode. speaker placement is another factor.

 i don't think it can be done because your reflections inside the room
will be too complicated (where as in headphones, there are no
reflections-- its pretty much a direct coupled system).

if you have 2 by 4 and drywall construction i also believe that along
with modes created by the air column, you will also have modes created
by the walls acting as drums. for block or cement walls maybe you could
replace the windows with infinite baffle woofers and mics.

maybe there is some phased array speaker arrangement. i would suspect it
would need a lot of energy.

k.


On 10/21/11 13:30, Michael Mossey wrote:
> On 10/21/2011 12:05 AM, Josh Moore wrote:
>> If there is a truck driving outside that's generating lots of
>> vibrations, those vibrations will be everywhere because they're
>> bouncing off lots of things and in a much larger space. 
>
> Ah, yes, but I'm only trying to nullify the *bass resonance modes*. 
> The truck noise across the spectrum will still be there, but the bass
> modes are 30 db+ louder than the direct truck noise.
>
> Mike
>
>
>
> Send bugs reports to the Sourceforge bug tracker
>            https://sourceforge.net/tracker/?group_id=81968&atid=564599
> Discussions of bugs and features can be posted here
> To unsubscribe, send email sympa@lists.bath.ac.uk with body
> "unsubscribe csound"
>



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On 10/21/2011 2:06 PM, Kelly Hirai wrote:
> if you have 2 bass bins you could set up an experiment i think. set up
> one outside to generate your bass mode. set up the other inside for
> cancellation.  using a constant frequency, try to dial in a phase /
> delay (for a single frequency its the same effect) amplitude of the same
> signal that cancels out the mode. speaker placement is another factor.
>
>   i don't think it can be done because your reflections inside the room
> will be too complicated (where as in headphones, there are no
> reflections-- its pretty much a direct coupled system).
>
I don't think the "reflections are complicated." It's a resonant mode of 
the entire room. The wavelength is larger than the room.

Mike



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