Nonetheless, it cannot fix cancellations. This is just physics, not opinion. You can only fix cancellations by lowering the energy of low frequency reflections back to the mixing position. You can do that by having a purpose built room, which few of us here have, or you can use bass traps. And, if you have enough bass traps to handle the cancellations, they are probably going to be dealing with most of the peaks as well.

If you are in a smallish, rectangular room and you have no bass traps, then it is pretty unlikely that you are really hearing accurately what is coming out of the monitors, at the low end anyway.

Hmmm.... I'm getting confused here...ARC, Bass Traps, room size

@Bit. where is his instructions?
 
 
I seem interested in the IK Multimedia ARC from watching the you tube videos about them. I always had a feeling that I may not be mixing or Eqing correctly because even when I like the way it sounds when mixing/EQing and then I listen to it in the vehicle, it sounds different. Though can any mic work with Ik Multimedia ARC software or does it have to be the mic they sell?
 
Is IK Multimedia the only program that does this kind of thing?

Dean's right, ARC and its ilk can do nothing to combat resonant nulls. 

Here's what that means: Sound will bounce off walls, the floor and the ceiling, eventually coming back to meet itself. The direct sound and the reflected sound collide, and get added together. If they happen to be in phase, they'll get louder. If they happen to be out of phase, they'll subtract from one another and get quieter. This is what screws up the frequency response of your room.

At certain frequencies, the main signal and the reflected signal will meet completely out of phase with one another, causing them to cancel each other out ("destructive interference"). At that specific spot, and at that specific frequency, there is effectively no sound. That's called a null, a dead spot in the room and the ONLY way to treat it is to provide acoustical absorption so that the reflected signal has less energy to add to the original direct signal.

(Note that when nulls are very close together we don't experience them as silence, but rather as comb filtering. That hollow, in-a-pipe sound. That's nasty too, but easier to treat because we're talking higher frequencies. When we talk about nulls we're usually referring to low-frequency problems, where the nulls are far enough apart to create noticeable dead spots.)

If the primary signal and the reflection meet exactly IN phase with one another, then they add together and cause a resonant PEAK. Just the opposite of a null. (It's called "constructive interference".) In that case, you hear way too much of that frequency. ARC can help with that by reducing just that frequency from your speakers' output.

However, ARC cannot "fix" peaks for every position in the room. That's because at a given frequency, there will be peaks AND nulls at different points within the room. What ARC can do is reduce the peaks at one important position - the spot where you sit when you mix. To someone standing behind you, it might still sound like crap!

These are the reasons ARC isn't a complete solution, but rather the finishing touch you apply after addressing problems acoustically as best you can.

Dean's right, ARC and its ilk can do nothing to combat resonant nulls.

Here's what that means: Sound will bounce off walls, the floor and the ceiling, eventually coming back to meet itself. The direct sound and the reflected sound collide, and get added together. If they happen to be in phase, they'll get louder. If they happen to be out of phase, they'll subtract from one another and get quieter. This is what screws up the frequency response of your room.

At certain frequencies, the main signal and the reflected signal will meet completely out of phase with one another, causing them to cancel each other out ("destructive interference"). At that specific spot, and at that specific frequency, there is effectively no sound. That's called a null, a dead spot in the room and the ONLY way to treat it is to provide acoustical absorption so that the reflected signal has less energy to add to the original direct signal.
I don't know if this is related, but sometimes when I am mixing using my monitor speakers, sometimes it's like I can't hear on one side (e.g. my left ear is like deaf) But when I turn my head or move around, I can hear again.
(Note that when nulls are very close together we don't experience them as silence, but rather as comb filtering. That hollow, in-a-pipe sound. That's nasty too, but easier to treat because we're talking higher frequencies. When we talk about nulls we're usually referring to low-frequency problems, where the nulls are far enough apart to create noticeable dead spots.)

If the primary signal and the reflection meet exactly IN phase with one another, then they add together and cause a resonant PEAK. Just the opposite of a null. (It's called "constructive interference".) In that case, you hear way too much of that frequency. ARC can help with that by reducing just that frequency from your speakers' output.

However, ARC cannot "fix" peaks for every position in the room. That's because at a given frequency, there will be peaks AND nulls at different points within the room. What ARC can do is reduce the peaks at one important position - the spot where you sit when you mix. To someone standing behind you, it might still sound like crap!
 
So, "constructive interference" is when the direct sound and the reflecting sound are in phase and make it sound louder and "destructive interference" is when they are out of phase and either become softer or null?
 
ARC only helps with "constructive interference" and not "destructive interference"?
 
Please correct me if I'm wrong.

These are the reasons ARC isn't a complete solution, but rather the finishing touch you apply after addressing problems acoustically as best you can.
 
I mix and EQ in one spot where I sit all the time when I work on projects.

Put Ethan's test file into SONAR, the one that bit mentioned above, and play it. Walk around the room while it's playing and stand for a bit in different positions. You'll experience the phenomenon very viscerally. At various points if you stand in one place, you'll feel like your head is being squished, that something is trying to pull your head to one side, and that your head is being expanded. Move a couple steps in some direction and it'll be completely different. The room is full of peaks and cancellations and they are constantly moving as the test signal sweeps upwards in frequency. Once in a while it will go completely silent as you get into a complete null at some particular frequency.

Whatever you decide sharpdion, best of luck. The guys here know what they are talking about moreso than I do and I mean that sincerely....but I have experience with this plug because I own it.... and honest when I tell you....it truly works. Nulls, errors, issues, whatever the case, it truly works for me. I'll leave it at that.

-Danny

ARC could do a lot more if we all had 20 or 30 speakers surrounding us. The analysis work it does is very good... it's ability to use the data it collects is hampered by the fact that there are often only 2 or 2.1 speakers in the room.

When ARC literature speaks about advanced phase management I get all excited, but in some ways it's effectiveness is limited by the fact that we use so few speakers. Also ARC comes before the speaker's crossover... where as it would be a *whole bunch* more effective if it came AFTER the speakers' crossovers. You can see large speaker arrays with full biamping splits being used in this manner in any large venue these days. A small 2.1 system doesn't let you sculpt the air with any where near the detail of a true split multi driver system.

I'll bet ARC could be even more powerful if we all used more elaborate playback systems. :-)

best regards,
mike

This is why mastering rooms typically have more than one subwoofer. At one time I thought that seemed like a needless extravagance, but after reading Dr. Toole's book I understood why they do that. You'd actually benefit greatly from having 3 or 4 subwoofers in a room!

You could have at least waited a while and given one of my stalkers the chance to point out that I have no idea what I am talking about.

;-)

One trick they teach in home theater calibration is that the room response at a given position is reversable. I.e. if you take a sub and put it up on a stand at your head level at the mixing position, you can then go around and measure room response at various places along the floor. When you find the best spot, put the sub there and the response back at the listening position should be basically the same. So you can avoid the huge effort of moving a big sub around and remeasuring many times.

I've not proven to myself that this is true, but it would appear on the surface to be so. If you looked at it as reflection points, using say light, you would have the same reflection points from the head position off of each surface so as to see the sub as you would have looking from the sub to each point where you see a reflection back to the head position.

Presumably, once you found a good position for sub #1, you could take a plot of the frequency response, then start looking on the other side of the room for a position that yeilds as close as possible to an inverse response, right? So where one is weak the other is solid, and vice versa.
 
Though, in general, based on my own experience, I'd argue that you should think hard before using a sub at all in the sort of small rooms most of us have. It creates a lot of complications at the point where the speakers and sub start to crossover. I measured a bazzillion or so different variations back when (with lots of bass traps in place), and that crossover point, using lots of different slopes and frequencies, was messy as measured. I had a box that let me control the xover frequency and slope on both sides, so I could do lots of experiments. Get the xover frequency semi-clean and it would react with the frequencies above or below the xover to make the peaks and dips worse. Make it stop doing that and the xover frequency area would end up usually as a very visible comb filter.
 
Ultimately I sold it and just stuck with the HR824 mkIIs, which had plenty of low end for my needs and I could get a cleaner low end response with just them.