input signal / captation

If you want to manipulate an acoustic sound using electronic tools, the acoustic sound has to be picked up by some kind of microphone. Since different kinds of mics end up determining a big part of how the electronics sound, they are certainly worth discussing.

Note to self: Mics can be considered to be instruments themselves. Some of them can be 'played' directly (for instance by touching it) and have specific benefits that deserve to be explored.

The Shure SM57 is a very good all-round choice to record local sounds. The mic is typically used for recording a sound close to its source, when environmental noises or acoustical reflections are not necessary. This microphone causes a minimum of feedback and is very affordable. When recording leap/detach, we used SM57’s to record and process small noises in the piano and the drums. A great alternative to the SM57 is the Beyerdynamic TG D35.

Piano

To pick up an acoustic piano with its full frequency range, the SM57 was not sufficient. It delivers a thin, unsatisfying sound and you would have to boost the signal a lot to get a workable volume (consequently resulting in feedback difficulties – mainly when using effects like reverbs and delays). Experimenting with different piezzo microphones on the wooden soundboard of the piano led to choosing the Barcus Berry 4000It is described as a boundary microphone for piano’s and harps and it works just like it should. On its own it sounds flat and cold (because the sound of the vibrating wooden board itself is captured – there is no vibrating air involved), but it is very versatile to use as a source for effects. This piezzo/contact mic has the big advantage of not being susceptible to feedback, giving access to a sound source that is comparable to the jack output of an electric guitar.

A more ‘realistic’ sound is obtained when using condenser microphones. More acoustic reflections and environmental noises are captured. This means that recordings sound very good, but these microphones are very feedback responsive. They are hard to control in a context where the incoming audio is manipulated in real-time. In this research project, a pair of Line Audio CM3 condensers is used to live-sample a realistic stereo image of the sound in the room.

Condenser microphones pick up a lot of the sound in the room, thus all the music in the room is captured at once, not just one isolated element. Microphones like this make the bridge between the different players in the ensemble, making it possible to electronically process the whole ensemble as one unit. More about this later on.

Guitar

Different guitar types were used. Electric guitars don’t need extra attention because the electromagnetic pickups won’t create feedback easily. The acoustic guitars that were used have built-in microphones with a dedicated EQ-setting, which works out perfectly for our purposes.

The use of a resonator guitar – without pickup – was trickier. Different contact mics were used but none of them gave satisfactory results. In practice, those contact mics are commonly combined with a mic directed to the instrument (because the sound originates from different parts of the body). When recording leap/detach we used a pair of Shure SM81 in X/Y setup.

For playing live the resonator guitar was captured with a DPA d:vote Core 4099 Guitar, which is a supercadioid clip-on mic that is made especially for acoustic guitars. You can mount it where ever you want and the sound quality is great. The disadvantage is its price and the fixed position – you can’t play with distance and with the position of your instrument relative to the mic (resulting in controllable variations of timbre). A recurring issue is the dealing with feedback sensitivity that is associated with the use of condenser mics. Best is to keep the overall volumes under control, especially in terms of monitor levels. Other tricks involve the EQ’ing of monitor signals and ringing out the feedback frequencies of the main speakers. A lot of expertise about amplifying resonator guitars is shared by the great Bob Brozman here: Bob Brozman live sound hints.

Drums

Due to their responsive character, drumheads are very sensitive to feedback. When the skins are strained loose they tend to vibrate quickly in response to the sound in the room. Therefore it’s useful to equalize the incoming sound – on the computer –  before processing it. Contact mics prevent feedback from happening, but when you’re looking for a natural sound, these are often not satisfactory. Since you have to press them onto the skin firmly – to prevent the mic from coming off when you strike the skin – you get a sort of muffled sound. However, for processing purposes the quality of input sound is not always as important. For a workable sound you might need to boost the mic signal with a DI.

During the recording of the leap/detach album, an SM57 dynamic mic and Beierdynamic TG D35 were used for the processing of the snare and tom sounds. A clip-on Korg contact mic was used for processing the bass drum sound.

To capture the entire drums, a stereo mic placed somewhere in the middle of the kit – on top of the bass drum – can give a good result. As you don’t want to pick up too much of the other instruments, you might have to gate the incoming signal, which can cause difficulties when playing very subtilely sometimes.