Cleaning and Restoring Audio

One of the most common, and the most annoying, issues facing anyone working with audio is the existence of unwanted noises and sounds in audio clips. You may have a great audio clip, but it can be filled with background noises:

  • cell phones ringing,
  • chairs squeaking,
  • someone coughing
  • It may even be a constant noise, such as a hiss from a microphone,
  • clicks and pops

Removing a Sound

We can remove a sound that occupies the same time space as audio that you want to keep. This can be someone caughing, cellphone ringing or a chair squeaking.

Hum: Hum is a continuous low frequency sound, similar to the whirring of a low pitched motor. It has a typical frequency of 40-80 hz. Hum is generally caused by electrical interferences or when the recording equipment is not properly grounded. Cheap audio interfaces and microphones also introduce hum in the recordings

Hiss: In electronic devices, hiss is often caused when random electrons deviate from their intended path under the influence of heat. These deviated electrons manipulate the output signal voltage and thus an audio noise is created. Low quality recording equipment generally results in hiss. Hiss can also be due to environmental factors, like a/c, fans etc.
In magnetic tapes, noise often results because of the granular composition of the medium. The larger is the size of the magnetic particles, the more is the possibility of audio noise to appear in the medium.

Rumble: Another common audio noise. It is a low-frequency audio noise which results due to a random sound wave that exists between specific limitation points. A rumble is most noticeable in turntables where ball bearings create the noise. In order to avoid or minimize the rumble, only high quality turntables with slide bearings should be used. In some instruments, rumble filters are used to remove the noise. This low-frequency audio noise can create problems while playing records on audio systems and hence needs to be corrected.

Crackle: crackles are discontinuous and non-musical sounds. These irregular explosive sounds are very much similar to the sound that we often here during wood burns. Such type of sound distortion is usually caused by explosive aperture of small airways.. Crackles can be further divided into two categories considering their acoustic properties and they are fine and coarse. Fine crackles are generally highly pitched and less intense audio noises while coarse crackles are of low pitch and last for longer durations.