How to test tracking room response

Hi, I would like to know how to test the tracking room (not the control room) for its frequency response. Does anyone have any insight about this? e.g. where to place the measurement microphone, should I use a loudspeaker, where to place the loudspeaker, should I measure the speaker first, etc. And i would like to know what is the frequency response for a room that considered good, what are we aiming for for it to sound good? If it can be done, I'm considering buying the ETF measuring software. BTW my room is approximately 3,5mx5m, with angled walls, and some angled ceiling. Any help or suggestions are highly appreciated. Thanks in advance.

You can measure a tracking room the same way, and with the same metrics, as a control room. Put a capable full-range loudspeaker at one end of the room, and put the microphone near the other end. Obviously, where you place these will affect the measured response, but you'll still be able to see the peaks and nulls at bass frequencies, and see the long decay times due to lack of high frequency absorption etc. --Ethan

Thanks Ethan, As for speaker and microphone placement, are they should be facing each other across the room, or facing away from each other, or else? A friend once told me if he's not mistaken, that he saw the process where the acoustician put the loudspeaker at one corner of the room, with small genelec 1030 facing the corner, and microphone is across the room, but aiming at the ceiling. Is it right to do that? If different placing of speaker and microphone will result in different frequency response, which one will give me the better picture of the frequency response? Or should I take many measurements with different placing? Will they show some kind of similarity? BTW thanks for answering, read so much about you and your articles. It's a big pleasure learning from an expert here. :) Ari

Also, I recommend checking out Room EQ Wizard before you buy ETF. As with any music room, you are looking for the flattest possible frequency response, with an even reverb time at all frequencies.

bolehnggak wrote:

they should be facing each other across the room, or facing away from each other, or else?

I'd say they should face each other, pointing in toward the room. Otherwise the HF response will be greatly affected. --Ethan

You have received good information on testing frequency response. What value will it be for you? The response will show you what happens for that particlular sender (speaker) and receiver (microphone) location. Tracking rooms are judged more by their reflections, both early as discrete events and late bunched together as reverb or ambience. Because tracking is a subjective exercise, broad generalities are inappropriate. What is good for one instrument for one piece is bad for another. As an extreme case, a bathroom is bad, unless you want a small echoey sound. About the only the generality that can be made for tracking rooms is a low end with minimal isolated modes dominating the sound. Yes I did not write well damped low end, because some acoustic instruments sound better with greater re-enforcement from the room at low frequencies. what I am attempting to say, and I certain failing at, is to think through what you want the room to sound like and from that what the room measurable characteristics would look like like before measuring them and trying to interpret the results. Andre

Thanks Andre, I built my room almost 4 years ago. My tracking room is approximately 3,5m x 5m, with varying heights, and angled wall to avoid parallel surfaces. The walls and ceilings are lined with rockwools directly to the wall (no space between the rockwools and the wall), with wood floor but some part of the area is carpeted. Actually I'm still having doubts of what my room should sound like. Because I have no comparison of other studio with similar size. There are other studios with similar sizes, but compared to them, IMHO mine still sound better. I described my room as warm, the ambience is somewhat dry. I played drums, and I actually love hearing my drums in that room, due to its warmth sound. When I mic the drums, actually they sound quite good by themselves, but then I compared my recorded drum tracks to the commercially recorded dry drum tracks, especially the overheads, it seems that the commercial tracks are brighter, more open but not ear piercing, while my overheads had more low mid frequencies, and not enough high frequency details. So if I mix the overhead tracks, I tend to decrease the low mids approximately at 200-300Hz, which made things better, but if I raise the highs, they are brighter but starting to be ear-piercing, and when I got the openness that I 'm looking for, I had to turn down the 8kHz to reduce the piercing sound, which is unsatisfying to me. Well, it could be my lack of EQing skill. So I'm thinking that it might be better if it's done naturally, by treating the acoustics. Ari

AVare wrote:

what I am attempting to say

You said it fine, and the only thing I'd add is there are some live room characteristics that are universally best avoided. Mainly strong resonances and flutter echo. Yeah, sure, maybe once in a while you want that as an effect. So you add it with an FX box. But you certainly don't want high Q ringing added to all tracks recorded in a room. --Ethan

Ethan, I have more question, - If I'm measuring a room with a loudspeaker, should I play sweep tones or pink noise through the loudspeaker? Or maybe other sound that should be used? - Since the loudspeaker or the microphone itself isn't really flat in frequency response, how can we be sure of the result of the room response is accurate? Ari

bolehnggak wrote:

- If I'm measuring a room with a loudspeaker, should I play sweep tones or pink noise through the loudspeaker? Or maybe other sound that should be used?

If you use software it will have its own test signals and know what to do.

Since the loudspeaker or the microphone itself isn't really flat in frequency response, how can we be sure of the result of the room response is accurate?

Most measurement microphones are plenty accurate, even cheap ones. More here: Comparison of Ten Measuring Microphones Speakers are also generally much flatter than any room, though speakers do vary as to how low they go, and will have some deviations. The flattest affordable speaker I know of is the Mackie 824. --Ethan

For tracking room I usually measure reverberation time first. There are several indications by the ISOs on this matter but basically: The microphones shall be at least 1 m from room surfaces, including the floor. Sound sources are also located away from room boundaries and at a minimum calculated distance from the microphone. If the room is too dead one must use a barrier between the sound source and the mic to reduce the influence of direct sound. Low frequency behavior can be tested like Ethan said but that is a very general approach. Problem with tracking rooms is that you might not have a fixed source/listener placement. This makes thinks more complicated to understand but the truth is that they are some tracking rooms that have bass traps while others (usually larger tracking rooms) don't really need it. So you can also use your ears and a couple of random measurements in the room just to check if you have that necessity or not. Reverberation time can be measured with MLS, sweep as well as impulsive signal. I prefer an impulsive sound for large rooms due to background noise related problems but that is not your case. Frequency response I usually use sweep signal.

When I mic the drums, actually they sound quite good by themselves, but then I compared my recorded drum tracks to the commercially recorded dry drum tracks, especially the overheads, it seems that the commercial tracks are brighter, more open but not ear piercing, while my overheads had more low mid frequencies, and not enough high frequency details.

This might have to do with the lack of existence of diffusers in your room and the abuse of rockwool in it. I have said a million times here that a tracking room is not a control room.

When I mic the drums, actually they sound quite good by themselves, but then I compared my recorded drum tracks to the commercially recorded dry drum tracks, especially the overheads, it seems that the commercial tracks are brighter, more open but not ear piercing, while my overheads had more low mid frequencies, and not enough high frequency details. Regarding the above qoute, did the "dry" drum tracks recorded at commercial studios actually use the exact same mics and device to record to as you are using? If not you cannot actually compare it because even if they are "dry" tracks they might have been tracked through a neve or ssl console that added its character to the sound...... Just take that into consideration aswell.

Yes you are correct that you cannot compare both examples if the mics/recording chain are not the same... but I still say there's a lot of difference between a tracking room with and without diffusion and it plays a significant role in the recorded sound. If other acoustical eng. or persons want to create a tracking room without diffusers they are on their own right. I personally prefer to use them.

To ARI (bolehnggak) : Studio lu dimana bos?