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#1
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Scott Dorsey wrote: The notion is that by using gated impulse testing, you can get a response which is equivalent to the response that you'd get from a swept test in an anechoic chamber. The gated impulse effectively eliminates room reflections from the testing, and therefore is "anechoic" meaning without echoes. This can only be made to work with a driving point that itself can deliver very short impulses. A typical speaker isn't done radiating by the time reflections start arriving. But that can be compensated by measurement of the speaker first in really anechoic or hemi-anechoic conditions, inverting its impulse response and from that point on convolving all stimuli sent through the speaker with that inverse first. The speaker is idealized in the process. This won't work too well as a way to compensate speakers for monitoring because of latency issues involved in convolution but for measurement it works well. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#2
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Mic Frequency Response
Scott Dorsey wrote: A perfect impulse has an infinite width, which is a problem to get in the real world. Make that infinitessimal rather than infinite. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#3
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Chris Hornbeck wrote: So Bob's concern with fatter sparks is with getting a longer *time* of arc? Rather than amplitude? No, the discharge is still very quick even if long. What the length gives is LF energy. A spark is not an impulse exactly and the longer it is the closer it gets to one. A short spark is a high passed impulse. The spark is a heating phenomenon where a local region of air expands due to heat and there is a relationship between the amount of energy dissipated and the spectral content. An exploding wire is different in that a highly condensed material, a metal, is instantly turned into a gas of _much_ greater volume. The energy dissipated in the process is also much higher, kilojoules. You can project potatoes very long distances with one. :-) The only real advantage of impulsive sources over swept sin approaches is the typically omnidirectional nature of the pressure field if that is desired. In all other regards the swept sin is superior. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#4
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On Thu, 06 May 2004 00:25:11 -0700, Bob Cain
wrote: So Bob's concern with fatter sparks is with getting a longer *time* of arc? Rather than amplitude? No, the discharge is still very quick even if long. What the length gives is LF energy. A spark is not an impulse exactly and the longer it is the closer it gets to one. A short spark is a high passed impulse. So, for better low frequency energy output, the spark needs to last longer in time. The spark itself will still provide the sharp leading and trailing edges. OK so far? The spark is a heating phenomenon where a local region of air expands due to heat and there is a relationship between the amount of energy dissipated and the spectral content. And the spectral content is determined by how long (in time) that the arc occurs? And acoustic amplitude is related in some way to the physical size of the gap? Thanks, as always, Chris Hornbeck |
#5
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Bob Cain wrote:
The only real advantage of impulsive sources over swept sin approaches is the typically omnidirectional nature of the pressure field if that is desired. In all other regards the swept sin is superior. if I'm not mistaken, with a bit of math you can convert an impulse response to a frequency response and vice versa, with the practical limitations of spark size limiting the low-frequency response measurement. swept sines seem like an anachronism when you have fourier at your disposal; what am I missing? -- Aaron J. Grier | "Not your ordinary poofy goof." | "someday the industry will have throbbing frontal lobes and will be able to write provably correct software. also, I want a pony." -- Zach Brown |
#6
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Aaron J. Grier wrote: Bob Cain wrote: The only real advantage of impulsive sources over swept sin approaches is the typically omnidirectional nature of the pressure field if that is desired. In all other regards the swept sin is superior. if I'm not mistaken, with a bit of math you can convert an impulse response to a frequency response and vice versa, with the practical limitations of spark size limiting the low-frequency response measurement. swept sines seem like an anachronism when you have fourier at your disposal; what am I missing? That you can do the same thing exactly with a swept sin. You just calculate the cross correlation of the response with a slight variation of the stimulus (using Fourier magic) and, voila, out pops the impulse response! The advantage of swept sin over impulse methods is noise immunity. You have much more energy in the response from which to calculate the IR than you do in a real impulse. It's advantage over pseudo random noise sequences is that spectral components due to non-linear distortion are separable using the swept sin. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#7
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OldBluesman wrote:
If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. OldBluesman Kind regards Peter Larsen -- ******************************************* * My site is at: http://www.muyiovatki.dk * ******************************************* |
#8
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OldBluesman wrote:
If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. OldBluesman Kind regards Peter Larsen -- ******************************************* * My site is at: http://www.muyiovatki.dk * ******************************************* |
#9
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Peter Larsen wrote:
OldBluesman wrote: If an inexpensive mic has the same frequency response and frequency response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Same primary reason - their response curves exist in 3 dimensions. I heard an AES presentation by Earl Geddes about what it takes to truly record and store the full frequency response curves of a mic or speaker with sufficient resolution. 'Tain't trivial even using modern computer hardware, though he says he has a patent-pending solution... |
#10
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Peter Larsen wrote:
OldBluesman wrote: If an inexpensive mic has the same frequency response and frequency response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Same primary reason - their response curves exist in 3 dimensions. I heard an AES presentation by Earl Geddes about what it takes to truly record and store the full frequency response curves of a mic or speaker with sufficient resolution. 'Tain't trivial even using modern computer hardware, though he says he has a patent-pending solution... |
#11
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" Frequency response and sound of mic is no better correlated than
frequency response and sound of loudspeaker. OldBluesman Kind regards Peter Larsen" Not true, you just need to see enough different kinds of measurements and learn how to read them. Expect to see more info on this in the coming years as major mic mfg's work w/the AES to create more useable standards to address your very comment. regards, David Bock Soundelux Microphones |
#12
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" Frequency response and sound of mic is no better correlated than
frequency response and sound of loudspeaker. OldBluesman Kind regards Peter Larsen" Not true, you just need to see enough different kinds of measurements and learn how to read them. Expect to see more info on this in the coming years as major mic mfg's work w/the AES to create more useable standards to address your very comment. regards, David Bock Soundelux Microphones |
#13
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Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#14
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Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#15
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Bob Cain wrote:
Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Since we've covered linear distortion, that leaves nonlinear distortion and noise. Noise as currently specified is not as revealing as it could, because mic have different noise spectra. In general, it seems like mics have relatively low nonlinear distortion as a rule, at least until the diaphragm bottoms, the transformer saturates, or the electronics clip. |
#16
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Bob Cain wrote:
Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Since we've covered linear distortion, that leaves nonlinear distortion and noise. Noise as currently specified is not as revealing as it could, because mic have different noise spectra. In general, it seems like mics have relatively low nonlinear distortion as a rule, at least until the diaphragm bottoms, the transformer saturates, or the electronics clip. |
#17
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"Bob Cain" wrote in message
... Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Distortion. Phase response. Hysteresis. Peace, Paul |
#18
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"Bob Cain" wrote in message
... Peter Larsen wrote: OldBluesman wrote: If an inexpensive mic has the same frequency response and frequence response curve as an expensive mic, what is the advantage of purchasing the expensive mic? Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. Then what other physical phenomenon accounts for the sound? Distortion. Phase response. Hysteresis. Peace, Paul |
#19
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"Then what other physical phenomenon accounts for the sound?
stortion. Phase response. Hysteresis." 3 of the above is an example of 1 and 2 would be seen as freq responce. The biggest differences are noise and pickup pattern if the mic is not overdriven. Two omins with the same freq responce and other things being equal will sound the same, for example. |
#20
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"Then what other physical phenomenon accounts for the sound?
stortion. Phase response. Hysteresis." 3 of the above is an example of 1 and 2 would be seen as freq responce. The biggest differences are noise and pickup pattern if the mic is not overdriven. Two omins with the same freq responce and other things being equal will sound the same, for example. |
#21
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"Then what other physical phenomenon accounts for the sound?
stortion. Phase response. Hysteresis." 3 of the above is an example of 1 and 2 would be seen as freq responce. The biggest differences are noise and pickup pattern if the mic is not overdriven. Two omins with the same freq responce and other things being equal will sound the same, for example. |
#22
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Arny Krueger wrote: Since we've covered linear distortion, that leaves nonlinear distortion and noise. Yep. Noise as currently specified is not as revealing as it could, because mic have different noise spectra. And don't, in general, color the sound of the mic. It's additive and at low levels. In general, it seems like mics have relatively low nonlinear distortion as a rule, at least until the diaphragm bottoms, the transformer saturates, or the electronics clip. Yes, condensers are much lower than any speaker you might listen on. Since it seems that every factor which could affect the sound of a mic has been ruled out, I guess were down to magic. Often happens with mics. Too often. Oh, by frequency response I presume both magnitude and phase were implied. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#23
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Arny Krueger wrote: Since we've covered linear distortion, that leaves nonlinear distortion and noise. Yep. Noise as currently specified is not as revealing as it could, because mic have different noise spectra. And don't, in general, color the sound of the mic. It's additive and at low levels. In general, it seems like mics have relatively low nonlinear distortion as a rule, at least until the diaphragm bottoms, the transformer saturates, or the electronics clip. Yes, condensers are much lower than any speaker you might listen on. Since it seems that every factor which could affect the sound of a mic has been ruled out, I guess were down to magic. Often happens with mics. Too often. Oh, by frequency response I presume both magnitude and phase were implied. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#24
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Arny Krueger wrote: Since we've covered linear distortion, that leaves nonlinear distortion and noise. Yep. Noise as currently specified is not as revealing as it could, because mic have different noise spectra. And don't, in general, color the sound of the mic. It's additive and at low levels. In general, it seems like mics have relatively low nonlinear distortion as a rule, at least until the diaphragm bottoms, the transformer saturates, or the electronics clip. Yes, condensers are much lower than any speaker you might listen on. Since it seems that every factor which could affect the sound of a mic has been ruled out, I guess were down to magic. Often happens with mics. Too often. Oh, by frequency response I presume both magnitude and phase were implied. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#26
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#27
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#28
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Bob Cain wrote:
Oh, by frequency response I presume both magnitude and phase were implied. Since the use of multiple mics in the same sound field is common, and the outputs are frequently added, phase is much more important than usual. |
#29
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Bob Cain wrote:
Oh, by frequency response I presume both magnitude and phase were implied. Since the use of multiple mics in the same sound field is common, and the outputs are frequently added, phase is much more important than usual. |
#30
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Bob Cain wrote:
Oh, by frequency response I presume both magnitude and phase were implied. Since the use of multiple mics in the same sound field is common, and the outputs are frequently added, phase is much more important than usual. |
#31
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Mike Rivers wrote: It's really all about frequency response, no any single frequency response curve accurately characterizes the sound of a microphone, other than perhaps a true omni mic (and there are darn few of those). Yep. Its the response as a function of frequency, angle of incidence to the plane of the diaphragm and the rotation angle about the axis. I would dearly love to find some real data measurments, taken at an incidence resolution of a few degrees, which would disclose the spatial frequency response of any directional mic but while we claim that it is such a big factor, I have never seen and have looked hard, for any real data to back that up. I would be especially interested in such data from a few well known mics for comparative analysis. Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size but I need data (or the time to gather it some day) to prove or disprove that. The frequency response, magnitude and group delay, encompasses the transient response. Any system's response to the shortest transient is isomporphic to its frequency response. People usually think "phase" but for audio and I wish we could change that. It's really group delay or time dispersion that we hear and are interested in. Phase was of interest for closed loop systems wherein the whole frequency domain thing was developed and phase gave information about stability, but for open loop systems and especially with respect to perception it's all about dispersion or group delay as a function of frequency. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#32
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Mike Rivers wrote: It's really all about frequency response, no any single frequency response curve accurately characterizes the sound of a microphone, other than perhaps a true omni mic (and there are darn few of those). Yep. Its the response as a function of frequency, angle of incidence to the plane of the diaphragm and the rotation angle about the axis. I would dearly love to find some real data measurments, taken at an incidence resolution of a few degrees, which would disclose the spatial frequency response of any directional mic but while we claim that it is such a big factor, I have never seen and have looked hard, for any real data to back that up. I would be especially interested in such data from a few well known mics for comparative analysis. Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size but I need data (or the time to gather it some day) to prove or disprove that. The frequency response, magnitude and group delay, encompasses the transient response. Any system's response to the shortest transient is isomporphic to its frequency response. People usually think "phase" but for audio and I wish we could change that. It's really group delay or time dispersion that we hear and are interested in. Phase was of interest for closed loop systems wherein the whole frequency domain thing was developed and phase gave information about stability, but for open loop systems and especially with respect to perception it's all about dispersion or group delay as a function of frequency. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#33
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Mike Rivers wrote: It's really all about frequency response, no any single frequency response curve accurately characterizes the sound of a microphone, other than perhaps a true omni mic (and there are darn few of those). Yep. Its the response as a function of frequency, angle of incidence to the plane of the diaphragm and the rotation angle about the axis. I would dearly love to find some real data measurments, taken at an incidence resolution of a few degrees, which would disclose the spatial frequency response of any directional mic but while we claim that it is such a big factor, I have never seen and have looked hard, for any real data to back that up. I would be especially interested in such data from a few well known mics for comparative analysis. Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size but I need data (or the time to gather it some day) to prove or disprove that. The frequency response, magnitude and group delay, encompasses the transient response. Any system's response to the shortest transient is isomporphic to its frequency response. People usually think "phase" but for audio and I wish we could change that. It's really group delay or time dispersion that we hear and are interested in. Phase was of interest for closed loop systems wherein the whole frequency domain thing was developed and phase gave information about stability, but for open loop systems and especially with respect to perception it's all about dispersion or group delay as a function of frequency. Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#34
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Bob Cain wrote:
Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size [ ... ] Two early morning thoughts: [a] The response actually heard on a recording will be somewhere between a microphone's on-axis response and its diffuse-field response, but how close it is to the one curve or the other depends on the miking distance and the recording environment. Diffuse-field response usually ends up being more important to the sound than most people seem to expect. Even in a close-up recording, more off- axis sound energy is picked up, and is heard in the result, than most people seem to think will occur. With moderately distant miking or in classical music-style recording which can be truly distant, the on-axis sound energy is a small fraction of the total. [b] The capsule's design and construction has a huge effect on its polar response at various frequencies, and this can't be predicted from its size alone, especially in pressure gradient transducers. The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. --best regards |
#35
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Bob Cain wrote:
Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size [ ... ] Two early morning thoughts: [a] The response actually heard on a recording will be somewhere between a microphone's on-axis response and its diffuse-field response, but how close it is to the one curve or the other depends on the miking distance and the recording environment. Diffuse-field response usually ends up being more important to the sound than most people seem to expect. Even in a close-up recording, more off- axis sound energy is picked up, and is heard in the result, than most people seem to think will occur. With moderately distant miking or in classical music-style recording which can be truly distant, the on-axis sound energy is a small fraction of the total. [b] The capsule's design and construction has a huge effect on its polar response at various frequencies, and this can't be predicted from its size alone, especially in pressure gradient transducers. The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. --best regards |
#36
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Bob Cain wrote:
Intuition tells me that the on axis response is the predominant factor and that the angular variations from that are going to be a very similar function across microphones of similar size [ ... ] Two early morning thoughts: [a] The response actually heard on a recording will be somewhere between a microphone's on-axis response and its diffuse-field response, but how close it is to the one curve or the other depends on the miking distance and the recording environment. Diffuse-field response usually ends up being more important to the sound than most people seem to expect. Even in a close-up recording, more off- axis sound energy is picked up, and is heard in the result, than most people seem to think will occur. With moderately distant miking or in classical music-style recording which can be truly distant, the on-axis sound energy is a small fraction of the total. [b] The capsule's design and construction has a huge effect on its polar response at various frequencies, and this can't be predicted from its size alone, especially in pressure gradient transducers. The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. --best regards |
#37
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David Satz wrote: The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. David, do you know of any source of full band polar measurement data on that or other mics? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#38
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David Satz wrote: The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. David, do you know of any source of full band polar measurement data on that or other mics? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#39
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David Satz wrote: The Neumann U 87 for example has a rather drastic (but reasonably smooth) loss of high-frequency response off axis, while other microphones of similar size may have bumpy, elevated high frequency response off-axis. That matters a lot to the overall character of a mike's sound in a room. David, do you know of any source of full band polar measurement data on that or other mics? Bob -- "Things should be described as simply as possible, but no simpler." A. Einstein |
#40
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David Bock wrote:
" Frequency response and sound of mic is no better correlated than frequency response and sound of loudspeaker. OldBluesman Kind regards Peter Larsen" Not true, you just need to see enough different kinds of measurements and learn how to read them. 30, 60, 90, 120, 180 degrees off axis response curves help. But static frequency response does not reveal things like membrane and housing resonances. Add waterfall diagrams and then things begin to get correlated. With static curves it is only possible to see that some mic has "a problem" at say 5 and at 12 kHz, because front to rear separation is poorer, but not positively whether it is a problem with a resonance. And all of that is still not the response in terms of tonal balance of recorded sound, to some extent because some "issues" are catered for in the positioning and angling of the actual mics in question. Some mics, such as those I use and could afford second hand, ARE better at having a violin slight off of their axis ... Expect to see more info on this in the coming years as major mic mfg's work w/the AES to create more useable standards to address your very comment. Very good news, thanks! regards, David Bock Soundelux Microphones Kind regards Peter Larsen -- ******************************************* * My site is at: http://www.muyiovatki.dk * ******************************************* |
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