This is probably one of those dumb questions and I'm probably not asking it correctly but...

Can reflections in a small room cause a single mic to record a signal that is out of phase with itself? Here's why I ask the question. When I play through my guitar amp live I hear a nice strong midrange, a nice high end and low end. Everything is there and it sounds great. However, when I record the amp I get a strong high and low end but the mid just seems to disappear. The mids aren't nearly as strong in the recorded track as they are live.

Edited by amiller (15/05/12 07:37 PM)

Phase cancellation can only happen when 2 signals are mixed together. when the peak of a waveform is scene at the same time as a dip or trough in the second waveform. which means when they are summed together they result in 0 or phase cancellation. this is only in a perfect scenario that we have a "perfect" phase cancellation.

so it wont be caused by the microphone its self.

what is possibly is the sound cancelling itself in the room itself. caused by the sound of your guitar bouncing back off walls then interfering with itself! But in my experience (granted fair limited experience) this will generally just be bass frequencies.

what ide recommend (someone more knowledgeable then me will probs recommend something better. but try turning the amp down slightly and moving it round the room. then try micing up the speaker cone in different position as they lead to different tones.

you could also try some acoustic treatment in the room but i am defiantly not much help there sorry.

hope that helps

Jack

Yep, the reflection bouncing off the walls interferes with the direct sound arriving at the mic. This can present as a hollow or boxy sound, or just some nastiness at a certain frequency. It's similar with drums. The room is very important part of a lot of recorded sound. but you need to position the source and the mic in such a way that the room reinforces the fundamental rather than cancelling it. Very small spaces tend to be problematic, while large spaces can suffer from the problem that early reflections are so delayed that they don't provide reinforcement. How much this matters depends...With a drum kit, which relies a lot of early reflections for density and a sense of '3D' it can be a big problem. With a distorted guitar amp, you'll most likely find that a lack of early reflection is even an advantage.

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Quote Jack Ruston:

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Yep, the reflection bouncing off the walls interferes with the direct sound arriving at the mic. This can present as a hollow or boxy sound, or just some nastiness at a certain frequency. It's similar with drums. The room is very important part of a lot of recorded sound. but you need to position the source and the mic in such a way that the room reinforces the fundamental rather than cancelling it. Very small spaces tend to be problematic, while large spaces can suffer from the problem that early reflections are so delayed that they don't provide reinforcement. How much this matters depends...With a drum kit, which relies a lot of early reflections for density and a sense of '3D' it can be a big problem. With a distorted guitar amp, you'll most likely find that a lack of early reflection is even an advantage.

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So, how do I address the issue in my particular case?

Move the amp. Start next to a wall. Then move away from the wall in 6 inch steps and see what happens.

Once you have a spot in the room where the amp is working with the room, try moving the mic for the best sound.

If you have a lot of high frequency and mids flying around you might want to dampen that stuff down. Try propping a matress up against the wall, big cushions, that sort of thing.


J

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www.jackruston.com