levels

Summary

Levels is a multimedia project involving the measurement of of energy found in various physical phenomena such as sound and electromagnetic radiation (radio waves, light, etc).

Frequency dependent energy is found in sound.

Using frequency selective filters, one may apply gain or reduction on acoustic energy over a selected range of frequencies. In addition, this gain may be varied over time based on the analysis of the signal. By providing a time varying gain we may make soft passages softer and louder passages louder. Doing so lowers the perceived noise floor and simultaneously provides a dynamic range that exists in real life but is lost by recording equipment.

For example, if the audio signal has a predominance of energy at lower frequencies (like an upright bass produces), then we can apply a filter to isolate the low frequencies and then apply a time varying gain to just the low frequencies- the result is a 'smooth and clean' sounding bass that sits where it should in the mix.

Using the idea of frequency selective, time varying gain, we can effect different portions of the audible frequency range uniquely and increase the overall perceived level in a more pleasing way. While beauty is in the eye of the beholder, there are some fundamentals associated with applying frequency selective, dynamic (time varying) gain during the mastering phase of a recording:

• Frequency band filters should be linear phase
• Dynamic processing should not impart a new 'character' to the sound

Here is an example of frequency selective, dynamic gain as implemented in the excellent Sonitus Multiband Compressor which was originally developed by Rune Johnsrud with Ultrafunk (and is now owned by Cakewalk, which only writes software for Windows):

Todo

• Make clips shorter
• Make center control
• Show levels using ITU P.56 Speech Level Meter.
• Show levels using 1/3 octave band filters.