On the last page, objective and measurable parameters of waves were introduced. We are not going to belabor the point this week, but there are some subtle differences in how we talk about this qualities depending on whether we in acoustics land or psychoacoustics land.
Frequency is the objective measure of how many cycles per second occur in a signal or wave. It is described numerically with respect to the Hertz unit.
However, when we are talking in music and perception land, we will often describe sounds with regard to their pitch or note name (i.e. one of the notes that make up the western 12-note octave: C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab, A, A#/Bb, B). However, the qualities that help us distinguish a sound event as a C or F# are subjective, and do not entirely describe the physics-based acoustic qualities of a sound. The reasons for this are greater than I want to get into now. But, it is important to remember, that although there is a relationship between frequency and pitch or note-name, they are not interchangeable.
Like the relationship of Frequency to Pitch, Loudness is subjective and can be considered as the subjective way we perceive of a sound’s amplitude.
Another important difference between loudness and a waves amplitude, is that amplitude describes the max or peak of a wave. Whereas loudness is typically describing an average loudness. Since sound and our perception of sound are time-dependent, we tend to average volume of sounds. This results in our perceiving of sounds as being softer than their loudest peak levels.
There are generally two ways of describing loudness. The first is RMS, which stands for Root-Mean-Square. This method adds up all amplitude values for a defined period of time, squares them, calculates the mean, then finally calculates the square-root. The RMS method is useful for understanding some qualities about the average loudness of a signal, but has not been found to map well to our perception of hearing.
The second method for describing loudness is LUFS (pronounced as a word). This acronym stands for Loudness Units relative to Full Scale. Like dBFS, LUFS are used to represent the the loudness of a digital audio file, below 0dBFS. LUFS are calculated using curves over the entire spectrum, which match more closely to the way we actually hear.
Please read from an Introduction to Computer Music:
Please read and complete the test questions from the following lessons in “Sound Waves” from The Physics Classroom