Music Technology A Guide to Microphones

Transcription

1 Music Technology A Guide to Microphones As part of your Music Technology coursework you have to record a commercially available song using a variety of close-mic and DI (direct inject) techniques. In this process you will to record a drum kit using a basic ambient/close-mic setup and use overdub and punch in techniques to complete you multi-track recording. Here are some points to consider: Microphone selection All microphones have different characteristics and you should experiment with them to see which ones you prefer. There are two main types of microphone. Condenser Microphone Wide, extended and generally more linear frequency response Detailed, clear sound with good high frequency response Sensitive with good transient response Phantom powered (+ 48 V) Fragile so handle with care! High output levels mean less gain required at the mixer Dynamic Microphone More colouration in the frequency response Good for high SPL s (high volume) Slow transient response Robust and reliable Quite low output needing high gain at mixer Low level of performer handling noise For the drum kit overheads it is appropriate to use two identical condenser microphones. This gives the sound for the whole kit focusing on the high-end cymbals and hi-hats. For the close miking of the drums is will be necessary to use dynamic microphones as these can handle higher SPL s (sound pressure levels) without distorting.

2 Microphone pickup patterns Omni directional Exhibit a wide, flat, extended frequency response Give good pickup of low and high frequencies Will pick up a lot of room reverberation Poor isolation of sound source Not affected by proximity effect Cardioid Rejects reverberation, background noise and spill Gives better isolation Good for stereo coincident or near- coincident miking Exhibits the proximity effect The cardioid has the widest front angle pickup and best rear rejection. Hypercardioid has the most side rejection, the most isolation and the most rejection in terms of reverb, spill and background noise. Bi-directional Good front and rear pickup, with maximum rejection of sound arriving at the sides The pickup pattern you use will depend on how you place your microphones in relation to the sound source and the venue. In general a standard cardioid pattern will produce good results

3 Microphone Positioning When you carry out a recording of this nature you are effectively attempting to recreate for the listener the actual experience of being in the venue sitting in front of the ensemble you are working with. The success of this often comes down to the careful positioning of the selected microphones to achieve the best result. Mic placement allows you to control: A sense of distance from the performers The balance between the instruments The stereo image or the panning of the instruments. Here are some methods of mic placement that you can use: X-Y Coincident pair This method is the easiest one to get good results. This setup involves using two matched cardioid microphones. They are placed close together and are angled at about 60 to 120 degree at the capsules. This angle will change the coverage area. Many engineers use 90 degrees and super-cardioid. The height of the mics also changes the sound. This miking technique is also called Coincident Pair Miking. The closer the mics are to the sound source the better or more 'stereo' the sound is while moving them away gives you more of a mono room sound.

4 Spaced pair The mics themselves are placed 6 feet above the ground and 6 to 8 feet apart forward facing the ensemble. You can use either omnidirectional mics or cardioid. If you want less audience noise/sound then use the cardioid pattern. For better sound quality then Omni's usually work better but with the increase in background (reverb) and audience The problem that arises when using Spaced pair miking is that the delay times between the mics can result in comb filtering (a bad thing in this case). The signal path lengths being different cause this. This problem has been addressed using the X/Y configuration. Blumlein Pair The pair consists of an array of two matched microphones of bidirectional (figure 8) pickup pattern, positioned 90 from each other. The array is oriented so that the line bisecting the angle between the two microphones points towards the sound source to be recorded (see diagram). The pickup patterns of the pair combined with their positioning, delivers a high degree of stereo separation in the source signal as well as the room ambience. The Blumlein pair produces an exceptionally realistic stereo image, but the quality of recordings is highly dependent on the acoustics of the room and the size of the sound source.

5 General advice In general you want a good level of direct sound compared with the reverberant sound. Placing the mics where you would normally sit in the audience will give you too much reverb when listening over loudspeakers. The closer the mics are to the performers, the closer they will sound in the recording. Experiment with distance to achieve the best balance between closeness and clarity, and liveness and reverberence. Once you have arrived at an optimum distance for your microphones you need to consider the stereo imaging produced. If the stereo spread is too wide then adjust the angle of separation. If the image is too off-centre make sure your levels for both mics are equal and that they are pointing in the right direction. The position of your performers is critical as well. Once you have set up the microphones and connected them to the mixing desk you need to route them to a stereo recording bus. It is very important that you get a good record level but also to be aware of any dynamics that might cause the recording to clip and go into distortion. Let the performers run through the piece at least once so you know how loud they are going to play and adjust the recording levels accordingly. Evaluation Checklist Can I hear any background noise? Can I hear any distortion? Are the left and right channels balanced equally? Have I made good use of the dynamic range of the recording medium (levels too high or too low) Have I accurately captured the stereo field of the sound source? Can I hear each instrument clearly? Is the recording a good representation of the performance? The final result should be top and tailed at the beginning and end of the piece and normalized to the optimum level. This will be handed in with the submission booklet so take notes of your mic positions! Photos can also be used.