Contact Miking the Piano Family
Aiming to help musicians, studio engineers and home recordists to achieve the highest quality sound, this is the first in a series of articles in which we examine an innovative method of capturing the sound of commonly used acoustic instruments — starting with the piano — by using the C-ducer contact microphone.
Under perfect studio conditions, with a well-positioned pair of top quality microphones, excellent results can be achieved when recording the acoustic piano in mono. However, several factors can degrade the results.
The first and most obvious problem to overcome when recording in 'the front room' is that of background noise — the 4.52 from Finchley Road & Frognall beating unpleasantly with the upright Broadwood. To a major extent, the use of a contact mic avoids this problem; there may still be a little breakthrough from airborne sounds, but by far the major contribution to the signal is the vibration of the instrument soundboard. Beware, however, for some sources of vibration (especially low frequencies) are particularly adept at travelling up the body of the piano (through the floor and up to the soundboard via the legs of the instrument). Try standing the piano with each foot on a rubber (eraser), it will often help.
Particularly in the small or home studio, there is often no room for screens (let alone a booth), so separating the piano from other instruments is impossible with conventional mics. Once again, the C-ducer only picks up the instrument to which it is attached. Remember too, that if one track is being laid onto another, the use of a contact mic can minimise the building up of 'ambience'.
Several top studios currently use C-ducer in preference to conventional mics, and I spoke to some to find out why. Firstly, the stereo sound stage achieved using C-ducer can be much more dramatic than with open mics, it tends to lead to a 'larger than life' sound which, although probably inappropriate for classical recordings, can be very effective in rock and contemporary jazz.
The other reason for choosing the C-ducer was to avoid 'spillage'. Even though background noise is no problem in any of the studios I spoke to, the spillage of one instrument over into the mic of another certainly is. Whilst booths are used, they do alienate the musicians concerned and can affect the characteristics of the 'ambience' behind the sound of the instrument.
Interestingly, when I spoke to the band Toto, the reason they gave for using C-ducer in the studio, as well as on stage, is because they can talk to each other without the speech coming out on tape.
When it comes to equalising the signal from any acoustic instrument, care must be taken not to adversely affect the tone of the background ambience. The use of a contact mic overcomes this problem since its signal contains negligible ambience. On the negative side, however, the signal also has none of the reverberation of an open-mic signal (effectively the reverberation time is reduced to zero) and if a sound with some reverberation is required, this has to be inserted electronically.
The C-ducer piano system consists of (i) a preamp, either battery-powered and high impedance (HiZ) only, or phantom powered with balanced and HiZ outputs (a mains power pack can be purchased if no phantom power is available); (ii) a pair of C-ducer 'tapes'; (iii) handbook; (iv) reel of sticky tape. The professional version (the CX Series) is available in either mono or stereo configuration.
The tapes are positioned as shown in Figure 1 and attached with double-sided adhesive tape (supplied). Although the exact positioning of the tapes did not seem to be particularly critical, really meticulous users might like to try an interesting technique used by Sky's sound engineer, Andrew Jones. When about to 'C-duce' a new instrument (an unknown piano, or whatever), Andrew 'searches' the soundboard with a doctor's stethoscope, and claims that it is infallible for finding the optimum position to stick the tapes.
Probably the most difficult keyboards to be miked are those in the family of early instruments — from harpsichord through celeste to the almost totally inaudible clavichord.
The C-ducer is a very quick and easy method of amplification and recording but be warned, if the pedal or key action is particularly noisy, it may be picked up by the C-ducer. All the users I spoke to were, predictably, impressed with the sound, and also with the ease and speed of setting up.
The stereo CX costs around £130 to the professional user and the battery powered piano system retails for £66.00 plus VAT.