A standard digital recording studio
The recording studio has seen a large number of changes since the introduction of digital technology. They have been one of the main sources of innovation in the music industry. The main reason is to become competitive. Artists wanting to record their music will choose the recording studio which will give them the best quality recording. Digital technology gives much more freedom to manipulate sound to create effects which will enhance the recording.
A Dynamic or moving coil microphone works in exactly the opposite way to a loudspeaker. A sound wave hits the thin membrane causing it to move backwards and forwards in a magnetic field. This movement causes an electrical current to flow inside the coil. This current can then be amplified to a useable level by a simple pre-amp. The microphone is omnidirectional which means it responds to sounds from all directions.
There are several advantages for using dynamic microphones
Dynamic microphones do have their disadvantages though.
A ribbon microphone works in a similar way to the dynamic microphone except that the coil and membrane is replaced by a thin conductive ribbon. The ribbon vibrates when a sound wave hits it causing a voltage to be generated across the ribbon. This small voltage is amplified to a useable level using a transformer. A good ribbon microphone operates in excess of 20kHz but only responds to sounds from in front or behind i.e. it is bi-directional. The ribbon can be very fragile which means that they are not often used in live performances.
A ribbon microphone is generally used to record classical music because it provides a smoother sound than many capacitor or dynamic microphones.
A capacitor microphone has two electrically charge plates. The sound wave causes the thin membrane to vibrate which alters the capacitance of the two plates. This change in capacitance can be converted to a voltage which can then be used for recording.
One of the drawbacks of using a capacitor microphone is that a separate 48V power supply is needed for operation. The main advantage is that the membrane can be made very thin which means excellent frequency response. Another advantage is that they can be made with any kind of response, omni-directional bi-directional etc.
In a traditional system the microphones are all attached to a large mixing desk. Traditional mixing desks can be very large and expensive. The main reason why mixing desks are this size is to accommodate the number of different sound controllers per channel. With a digital studio microphones are connected to analogue to digital converters and then by optical fiber to the digital signal processor (mixer) The use of a digital system allows for a virtual mixing desk which encompasses all the features of a traditional analogue mixing desk but can be operated using a simple point and click windows system. Many traditional sound engineers are opposed to this method as it lacks the feel of a physical system.
A digital mixer has to provide the three basic operations provided by an analogue mixer which are attenuating, mixing and selection of channels.
In an analogue system attenuation is achieved by simply using a potential divider connected to Vin and earth. This provides a complete range of values from 0V to Vin. The digital version works in a similar way. A potential divider is connected to a reference voltage and earth. The output of the potential divider is passed through an A/D converter. A multiplier then multiplies the two signals providing a range from 0V to Vin
In an analogue system mixing is achieved using a summing Op-Amp. In a digital system initially a multiplexer interleaves the channels then a full adder is used to sum the channels.
In an analogue system selection is achieved using a multipole switch. The digital equivalent is a De-multiplexer which is used to extract channels and an encoder which is used to select the desired channel.
At first sight it may seem that we are going to a lot of trouble just to overcomplicate an existing system which works well. The digital system allows for greater manipulation of the digital information providing access to many effects which were not possible under an analogue system.
In many digital systems there are still processes that are best implemented in an analogue fashion. In the recording process the use of compressors, which reduces the dynamic range of an incoming signal, and gates, which expand the dynamic range of an incoming signal, are still generally implemented using analogue circuitry. All effects involving time manipulation are implemented digitally.
The digital signal is split up into two paths. One path is left untouched and is passed directly to a mixer. The other path is known as the delay path. It is passed into RAM where it is stored for a short period. A microprocessor is then used to manipulate this data. The microprocessor has two main functions.
The signal is then fed-back to the input of the delay line so that multiple echoes can be set up and then the two signals are recombined.
Single delay creates a single echo and is often used to accentuate the rhythm of the music. It is achieved by setting the feedback, modulation depth and rate to 0. The delay of the echo can then be adjusted to repeat in time with the music. The next stage is to add a repeating echo. This is achieved by simply increasing the feedback.
Chorus provides a wide dynamic sound and is often used on strings and electric guitar. It is achieved by setting the delay to approximately 10ms and then using low depth modulation at a frequency of about 3Hz. It is then mixed half and half with the original signal. To provide extra depth to the sound the chorus can be panned to either the left or right channel.
Vibrato is an effect used by most musicians to create a richer fuller tone. It is most visible when watching a violinist. The violinist moves the finger which is playing the note back and forwards causing a slight periodic change in pitch. Vibrato is achieved in a similar way to chorus. The delay used is only a few milliseconds and the modulation is about 3Hz but the original signal is not used.
Phasing is an effect which is widely used. Two identical musical channels are allowed to drift in and out of phase creating a sense of movement. It is achieved in the same way as vibrato, but the original signal is also combined.
Flanging is a stronger form of phasing generating a characteristic 'whoosh' which if panned across both channels creates a sense of movement. It is achieved in by using a modulation period of about 1 Hz, a delay of about 10ms and a subtle use of feedback.
The DDL can be used to play samples. A user defined delay is used. The sample is played when the user releases the hold. This is often used for repetitive spoken lyrics.
It can be seen that with only slight alterations in input to the DDL a large number of effects can be created. In analogue systems phasing for example used to be achieved by playing two copies of the track on separate tape players and slowing down one of the tapes using the hand. Obviously this lacks the sophistication of the digital alternative.
Reverberation is a natural phenomenon which is caused by reflections of sound waves. The delay of the reflections describes the size of the room and the time taken for the decay of the signal describes the material that the waves are being reflected off. A small room with absorbent walls would create a signal with a fast decay and a fast build up of echo whereas a large room with reflective walls would create a signal which slowly decays and has a slow build up of echo. The effect can be quite subtle but the human brain can distinguish between a large and a small room by just hearing a sound.
Before digital technology reverberation was generated by either using a room with the desired characteristics or using artificial reverb generated using a plate. The plate is suspended and then driven by a transducer. Two contact transducers are used to pick up the signal which is then recombined with the original signal at the mixing desk. The effect is quite convincing as the vibrations in the metal plate closely simulate natural reverberations.
Creating electronic reverb is a very complex process. It has been shown that approximately 1000 to 3000 separate echoes are needed to create a convincing reproduction of natural reverb. The kind of reverb needs to be defined as well. Different materials have different frequency responses so different forms of digital filtering need to be implemented to allow the user choice over the kind of reverb used.
There are many digital reverberation systems available most of which are implemented using software. Digital filtering is much easier to implement using software as the filter's characteristics can be stored in a lookup table. Most systems have predefined reverberation characteristics. This may seem at first to be very restrictive but the subtle differences that can be made using a fully programmable system would not be noticeable in a complete mix.
During the production of a piece of music monitoring is of vital importance because it provides the sound engineer with many tools. It is possible to monitor just one track at a time so that the track can be set up precisely. The channels can then be recombined so the engineer can see how the mix is sounding. Monitoring requires the conversion of the digital signal back into analogue. A D/A converter is used so that monitoring using either studio monitors (loudspeakers) or headphones can be achieved. Headphones provide the sound engineer with detailed reproduction of the track being recorded but they lack the feel associated with a good pair of loudspeakers.
When using a recording studio cueing is very important. There are two main purposes. Cueing is used to relay messages between the sound engineer and the musician because the recording part of the studio is soundproofed from the mixing room. The other main use is when extra tracks are being laid on top of existing tracks. The musicain who is being recorded has a pair of headphones which are given the backing track. The musician can then play along as if the full band was there.
The final part of the studio process is the actual production of the master copy which will be used for replication. In modern digital studios this is usually implemented using a DAT machine, which is a digital tape recording system, or a Compact disc writer.