Waveform graphs
A graph of a waveform shows us how the displacement changes over time, between its maximum positive and maximum negative values and around a zero line
May also see waveform graphs that show change in voltage over time.
Logarithmic Scales
A logarithmic scale is used to represent orders of magnitude as a linear change
The decibel scale and the frequency values on a filter or EQ graph are examples of logarithmic scales.
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Waveform graphs
A graph of a waveform shows us how the displacement changes over time, between its maximum positive and maximum negative values and around a zero line
May also see waveform graphs that show change in voltage over time.
Logarithmic Scales
A logarithmic scale is used to represent orders of magnitude as a linear change
The decibel scale and the frequency values on a filter or EQ graph are examples of logarithmic scales.
Logarithmic Scales - EQ
EQs are organised in this way because of our greater sensitivity to lower frequencies and because doubling a frequency means moving an octave higher.
Logarithmic Scales - dB
The decibel is a unit of sound pressure level. It uses a logarithmic scale because our ears don’t respond to sound pressure in a linear way. Our ears hear logarithmically i.e. a chainsaw is many times louder (when measuring pressure and power) than a conversation, but we don’t percieve it like that
When we use dB to muasure sound pressure level, we can normally set meters to Peak or RMS mode
Because of the way in which we perceive sound, we will hear sounds with a consistently higher level as louder than those with a loud peak but no sustained volume
This type of psychoacoustics is why we sometimes hear a whole drum kit playing a beat as leader than a singer cymbal hit.
Peak
A transient measure of loudness
The meter will give a momentary measuer of the highest volume of the signal
Useful for setting input gains to avoid distortion, or to create pumping effects on compressors
RMS
Stands for Root Mean Square, an average measure of loudness
Much slower analysis than peak and is useful if you are looking for the average volume of something
Useful for measuring the overall volume of audio and is often used to gauge the volume of a track during the mastering process
Period
Frequency (measured in Hz), is the number of waveform cycles per second
The period of an oscillation is the amount of time a single cycle takes
The frequency of an oscillation is directly related to the period of the oscillation.
Where frequency = F and period = T
F = 1 / T
T = 1 / F
Frequency and musical intervals - Octave higher
The octave higher is always double the frequency of the original
SO
F = n x 2
Frequency and musical intervals - Octave lower
The octave lower is always half the frequency of the original
SO
F = n / 2
Perfect 5th higher
The perfect 5th higher is the mid-point between the original and octave higher
SO
F = n x 1.5
Perfect 4th higher
The perfect 4th is the same note name as a perfect 5th but an octave lower
SO
F = n x 0.75
Frequencies from the harmonic series
If you know (or can work out) the fundamental frequency, you can approximate the frequency of a note in the harmonic series
The fundamental frequency is also referred to as the first harmonic
We can calculate the frequency of higher harmonics by using the calculation:
Where Fh = Harmonic frequency
Where Ff = Fundamental frequency
Where n = number of harmonic
Fh = Ff x n
Calculating delay time from BPM
To calculate the delay time of a crotchet at 100BPM in seconds:
Delay time (s) = 60(s) / Crotchet beats per minute
Delay time (s) = 60 / 100
Delay time (s) = 0.6(s)
The delay time is for a crotchet (1/4)
For a quaver (1/8), the delay time would be half as much so 0.3s
For a minum (1/2), the delay time would be twice as much and so 1.2s