Topic by Professor Leandro Duarte

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Topic: Closed lid vs. Microphone inside or outside?

Hello, dear friends!

After some tests, I noticed that the piano lid generates the same effect when the microphone is inside or outside the piano. I think that the correct thing would be for the sound intensity to change when the microphone is outside a piano with the lid closed, but not with the microphone inside the piano.

What logic is there in reducing the sound intensity of a piano with the lid completely lowered when the microphone is inside the piano?

Thank you very much for your attention!

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Reply by Pianistically

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Re: Closed lid vs. Microphone inside or outside?

Professor Leandro Duarte wrote:

Hello, dear friends!

After some tests, I noticed that the piano lid generates the same effect when the microphone is inside or outside the piano. I think that the correct thing would be for the sound intensity to change when the microphone is outside a piano with the lid closed, but not with the microphone inside the piano.

What logic is there in reducing the sound intensity of a piano with the lid completely lowered when the microphone is inside the piano?

Thank you very much for your attention!

obviously it is just an hypothesis as we don’t how the intrisics of the mic/lid PTQ algorithm , but if the mics are  inside and the lid is closed , reflection of the sound in the lid could be in opposition of phase with the original signal and therefore reduce the amplitude of the wave . So in real acoustic , in all cases there is a variation of the wave signal when you change  the lid position , with mics inside or outside .

Reply by Professor Leandro Duarte

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Re: Closed lid vs. Microphone inside or outside?

Pianistically wrote:
Professor Leandro Duarte wrote:

Hello, dear friends!

After some tests, I noticed that the piano lid generates the same effect when the microphone is inside or outside the piano. I think that the correct thing would be for the sound intensity to change when the microphone is outside a piano with the lid closed, but not with the microphone inside the piano.

What logic is there in reducing the sound intensity of a piano with the lid completely lowered when the microphone is inside the piano?

Thank you very much for your attention!

obviously it is just an hypothesis as we don’t how the intrisics of the mic/lid PTQ algorithm , but if the mics are  inside and the lid is closed , reflection of the sound in the lid could be in opposition of phase with the original signal and therefore reduce the amplitude of the wave . So in real acoustic , in all cases there is a variation of the wave signal when you change  the lid position , with mics inside or outside .



I think it's a bug.

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Reply by Luc Henrion

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Re: Closed lid vs. Microphone inside or outside?

In real life, (I mean the recording of my real grand piano) I didn't find a big difference in level, but rather a difference in timbre. . Just my 2 cents.

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Reply by Pianistically

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Re: Closed lid vs. Microphone inside or outside?

Luc Henrion wrote:

In real life, (I mean the recording of my real grand piano) I didn't find a big difference in level, but rather a difference in timbre. . Just my 2 cents.

that’s because human ear is more sensitive to variations of frequencies than variation of db levels , but from a pure mathematical standpoint , it seems obvious than if a you have  a mic placed internally in a fixed position and you start releasing  the lid progressively from bottom closed  to full open position the  phasing  of the primitive  sound coming from the soundboard  and the sound coming form the reflection on the lid will vary during the lid travel therefore the overall level of sound captured by the mic will vary as well . The fact that the timbre changes is somehow a  collateral effect as some of the partials  will not be audible anymore because of the phase cancellation affecting their level to a point where they are not perceptible anymore by human ear , in other words , the overall audible spectrogram is indeed modified .

Reply by Luc Henrion

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Re: Closed lid vs. Microphone inside or outside?

Pianistically wrote:
Luc Henrion wrote:

In real life, (I mean the recording of my real grand piano) I didn't find a big difference in level, but rather a difference in timbre. . Just my 2 cents.

that’s because human ear is more sensitive to variations of frequencies than variation of db levels , but from a pure mathematical standpoint , it seems obvious than if a you have  a mic placed internally in a fixed position and you start releasing  the lid progressively from bottom closed  to full open position the  phasing  of the primitive  sound coming from the soundboard  and the sound coming form the reflection on the lid will vary during the lid travel therefore the overall level of sound captured by the mic will vary as well . The fact that the timbre changes is somehow a  collateral effect as some of the partials  will not be audible anymore because of the phase cancellation affecting their level to a point where they are not perceptible anymore by human ear , in other words , the overall audible spectrogram is indeed modified .

Of course, but I was surprised by the very, very small difference in level: the VU meters on my DAW more or less matched my ears ;-)

Luc Henrion's Website

Reply by Pianistically

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Re: Closed lid vs. Microphone inside or outside?

Luc Henrion wrote:
Pianistically wrote:
Luc Henrion wrote:

In real life, (I mean the recording of my real grand piano) I didn't find a big difference in level, but rather a difference in timbre. . Just my 2 cents.

that’s because human ear is more sensitive to variations of frequencies than variation of db levels , but from a pure mathematical standpoint , it seems obvious than if a you have  a mic placed internally in a fixed position and you start releasing  the lid progressively from bottom closed  to full open position the  phasing  of the primitive  sound coming from the soundboard  and the sound coming form the reflection on the lid will vary during the lid travel therefore the overall level of sound captured by the mic will vary as well . The fact that the timbre changes is somehow a  collateral effect as some of the partials  will not be audible anymore because of the phase cancellation affecting their level to a point where they are not perceptible anymore by human ear , in other words , the overall audible spectrogram is indeed modified .

Of course, but I was surprised by the very, very small difference in level: the VU meters on my DAW more or less matched my ears ;-)

interesting feedback .  Also I guess the effect is also depending of index of refraction of the lid itself  . Close reflection of a wave on a material with high level of refraction generates a π phase opposition and can lower the volume level considerably as opposed to a low level index of refraction . Wood absorbs more than what it reflects so the phase opposition is moderate so your observation is spot on