sound_designer
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MICROPHONES
With the plethora of microphones around you'd be surprised at how engineers all over the world seem to use the same mikes. Go surfing to all the studios and you'll find the same mikes in their mike list. I've got to state here that I'm not pushing any particular brand or type - I am not sponsored - so I'm only stating what I've observed over the years.
So how do they work? Basically all microphones have a diaphragm that vibrates when hit by sound waves. The vibration of the diaphragm is translated into an electrical signal that corresponds to the variation in the sound wave. That is why it is necessary to clean the diaphragms in your mikes on a regular basis as a build-up of dust, spit etc. will impede the vibration of the diaphragm and thus distort or colour the sound.
Part 1:
The Dynamic
In a Dynamic microphone, also referred to as a moving coil microphone, the capsule is rather like a speaker in reverse. The cone is the diaphragm and it has a coil attached that is suspended in a magnetic field. When the diaphragm vibrates the coil creates an electrical current. This is an entirely passive circuit as the magnet can be a permanent one so no external power is required.
The Condensor
On the other hand the Condensor microphone has two plates, one fixed and one moveable, that are each charged with a polarising voltage that creates a capacitor. The vibration of the plates creates a change in the distance between them which changes the capacitance and thus the sound wave is converted into an electrical current. In this case external power is required as there is an electrical circuit required to produce the polarising voltage. Because the current obtained is so small an amplifier circuit is also included.
Thus when using Condensor mikes an external power supply is required. This can be either a stand alone power supply for one or more mikes or it can be fed to the microphone from the console down the microphone cable and is commonly referred to as Phantom Power and is now standard at 48 Volts and all new consoles have that facility and usually consists of an on and off switch on the rear of the console or is an on/off option on each module. Incidentally, don't worry about sending phantom power to a dynamic microphone, it won't blow it up as the circuit is inactive in a dynamic mic situation.
The Valve Microphones
Finally I must say something here about Valve Microphones. As mentioned before, the signal from the diaphragm in a Condensor microphone is small and must be amplified before it reaches the console where again it is amplified further. It is within this area that signal deterioration can easily occur and therefore the quality of the microphone must also be judged by the quality of the first stages of amplification. In a valve microphone the Condensor stage is a standard condensor system but the amplifier section uses a valve circuit to amplify the current as opposed to a transistor circuit used in later models. When I first started as an engineer in 1966 all the Condensor microphones were valve and each had its own power supply. The introduction of the transistor microphone eliminated the need for power supplies because phantom power was invented for the purpose.
The other major factor in those days was signal to noise. The average tape recorder had a signal to noise ratio of around 58db as opposed to the 70+ with today's analogue recorders.(Mainly due to the improvement in the surfacing of tape.) With such a low signal to noise ratio we were always careful about the high end of our recordings because if you had to add it later you sacrificed your noise and increased hiss. So when the transistor microphone came out we all remarked "Far out!" (it was the 60's) listen to that top end!!" and immediately used them instead because records were getting brighter then. What we were hearing was the difference in distortion between a valve and a transistor. A valve distorts in the 2nd harmonic first whilst a transistor distorts in the 3rd harmonic. The 2nd harmonic distortion is smooth, we can handle it but 3rd harmonic distortion is hard and harsh to our ear hence the difference between the two. The valve appears warmer like a valve Marshall does compared with a transistor version.
Today, on the other hand, the top end and noise is not a problem as modern analogue tape recorders have good signal to noise ratios and our mike preamps are also quiet yet from another aspect it is. The top end of digital is extremely bright compared with analogue tape due to the inherent distortion of frequencies above 7kHz created by the slow sampling frequency of 44.1kHz which in reality produces close to a square wave above 10kHz I find it produces what I call digital fatigue. Rupert Neve was recently reported as saying that we will need to sample at 24 bit/192kHz to equal analogue. (We will eventually) Meanwhile the warmth of the valve acts with the harshness of digital and produces a great compromise, hence one of the reasons for the popularity of valve mikes today.
Alternatively engineers today will put a mike through a valve preamp which is the second stage of amplifying a mic signal. Once again it is the soft clipping of the high end that produces that warm sound. What a lot of manufactures do today is the put a valve within a transistor circuit thus obtaining the soft clipping of the valve with the improved signal to noise of the transistor circuits. I've even seen an ad for a CD player that has a valve circuit in it!!
-WILL CONTINUE.......
With the plethora of microphones around you'd be surprised at how engineers all over the world seem to use the same mikes. Go surfing to all the studios and you'll find the same mikes in their mike list. I've got to state here that I'm not pushing any particular brand or type - I am not sponsored - so I'm only stating what I've observed over the years.
So how do they work? Basically all microphones have a diaphragm that vibrates when hit by sound waves. The vibration of the diaphragm is translated into an electrical signal that corresponds to the variation in the sound wave. That is why it is necessary to clean the diaphragms in your mikes on a regular basis as a build-up of dust, spit etc. will impede the vibration of the diaphragm and thus distort or colour the sound.
Part 1:
The Dynamic
In a Dynamic microphone, also referred to as a moving coil microphone, the capsule is rather like a speaker in reverse. The cone is the diaphragm and it has a coil attached that is suspended in a magnetic field. When the diaphragm vibrates the coil creates an electrical current. This is an entirely passive circuit as the magnet can be a permanent one so no external power is required.
The Condensor
On the other hand the Condensor microphone has two plates, one fixed and one moveable, that are each charged with a polarising voltage that creates a capacitor. The vibration of the plates creates a change in the distance between them which changes the capacitance and thus the sound wave is converted into an electrical current. In this case external power is required as there is an electrical circuit required to produce the polarising voltage. Because the current obtained is so small an amplifier circuit is also included.
Thus when using Condensor mikes an external power supply is required. This can be either a stand alone power supply for one or more mikes or it can be fed to the microphone from the console down the microphone cable and is commonly referred to as Phantom Power and is now standard at 48 Volts and all new consoles have that facility and usually consists of an on and off switch on the rear of the console or is an on/off option on each module. Incidentally, don't worry about sending phantom power to a dynamic microphone, it won't blow it up as the circuit is inactive in a dynamic mic situation.
The Valve Microphones
Finally I must say something here about Valve Microphones. As mentioned before, the signal from the diaphragm in a Condensor microphone is small and must be amplified before it reaches the console where again it is amplified further. It is within this area that signal deterioration can easily occur and therefore the quality of the microphone must also be judged by the quality of the first stages of amplification. In a valve microphone the Condensor stage is a standard condensor system but the amplifier section uses a valve circuit to amplify the current as opposed to a transistor circuit used in later models. When I first started as an engineer in 1966 all the Condensor microphones were valve and each had its own power supply. The introduction of the transistor microphone eliminated the need for power supplies because phantom power was invented for the purpose.
The other major factor in those days was signal to noise. The average tape recorder had a signal to noise ratio of around 58db as opposed to the 70+ with today's analogue recorders.(Mainly due to the improvement in the surfacing of tape.) With such a low signal to noise ratio we were always careful about the high end of our recordings because if you had to add it later you sacrificed your noise and increased hiss. So when the transistor microphone came out we all remarked "Far out!" (it was the 60's) listen to that top end!!" and immediately used them instead because records were getting brighter then. What we were hearing was the difference in distortion between a valve and a transistor. A valve distorts in the 2nd harmonic first whilst a transistor distorts in the 3rd harmonic. The 2nd harmonic distortion is smooth, we can handle it but 3rd harmonic distortion is hard and harsh to our ear hence the difference between the two. The valve appears warmer like a valve Marshall does compared with a transistor version.
Today, on the other hand, the top end and noise is not a problem as modern analogue tape recorders have good signal to noise ratios and our mike preamps are also quiet yet from another aspect it is. The top end of digital is extremely bright compared with analogue tape due to the inherent distortion of frequencies above 7kHz created by the slow sampling frequency of 44.1kHz which in reality produces close to a square wave above 10kHz I find it produces what I call digital fatigue. Rupert Neve was recently reported as saying that we will need to sample at 24 bit/192kHz to equal analogue. (We will eventually) Meanwhile the warmth of the valve acts with the harshness of digital and produces a great compromise, hence one of the reasons for the popularity of valve mikes today.
Alternatively engineers today will put a mike through a valve preamp which is the second stage of amplifying a mic signal. Once again it is the soft clipping of the high end that produces that warm sound. What a lot of manufactures do today is the put a valve within a transistor circuit thus obtaining the soft clipping of the valve with the improved signal to noise of the transistor circuits. I've even seen an ad for a CD player that has a valve circuit in it!!
-WILL CONTINUE.......
