Thursday, August 4, 2011

Where distortion can creep into audio recordings

During audio recording there are a number of places where audio distortion can creep in. We are going to identify where these points in the recording chain are. Firstly a microphone will have a physical limitation as to how much it's diaphragm can move before it no longer represents the acoustic signal being produced. So ensure that the maximum SPL capability of your microphone is in excess of the instrument being recorded.

The next factor is the electronics in the mic, if this distorts you need to apply a pad switch if the mic has one. This will reduce the level of distortion in the mic.(and coming from the microphone) Then you will be plugged into a microphone preamplifier which in turn may distort, again you can use a microphone pad switch which often reduces the signal by 10 or 20dB so its good option for you. Sometimes microphone preamplifiers will have a pad switch built in as well, this can be useful if extra attenuation is required to keep the mic level down. Ensure that you have your gain structure correct on your microphone preamplifier signal meter, audio peaks should hit 0vu so there is some headroom if there are unexpected louder peaks. Ensure that you have your audio interface set to receive the correct level at the line inputs. (It may be possible to switch between +4dbu and -10dBv either on the audio card physically or within a software applet, +4dBu being a professional level standard and -10dBv being a semi-pro reference level.

When you record ensure you record at 24 resolution in your digital audio workstation and ensure that you signals peak around -18dBFS to -12dBFS on a digital meter, there is no need to record at a level any higher than this when recording at 24bit as the quality will still be very high. During mixing it will be a good plan to peak a kick drum at -18dBFS on the stereo ouput when you begin to mix the music. Balance the mix against this kick drum as a reference then you will not exceed digital zero and clip the output master bus (another potential form of distortion). By following the above guidelines you will have cleaner and clearer music recordings. It always be peaceful if you get clear audio recording.

Ultimately distortion is the result of a system or physical piece of equipment which has gone beyond it's design capabilities. Once the capability has been exceeded the device or system can no longer represent the audio signal in the system (or that to be recorded) with any accuracy. This is why in audio engineering schools there will be a big emphasis on not recording too hot and leaving sufficient headroom for the device in question. I hope these suggestion will help you to record distortion free audio.

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