Join Brian Lee White for an in-depth discussion in this video Measuring amplitude , part of Audio Foundations: EQ and Filters.
We've discussed frequency as the oscillation speed of the soundwave, but what about the other dimension, amplitude? A waveform's amplitude, or amount of push and pull, can be measured using sound pressure level, or SPL. SPL is a logarithmic scale measured in decibels, or dB, above a standard reference level. The standard reference level most commonly used for the starting point of 0 dB is 20 micropascals RMS.
Pascals are unit of measurement for pressure or stress. 20 micropascals is usually considered the threshold of human hearing at 1k. The decibel scale is a logarithmic measurement scale. Turning up an audio signal's volume by 1 dB is basically imperceptible. For most of us, it takes at least a 3 dB increase for us to notice it. However, because of its logarithmic scaling, the loudness escalates quickly.
A 10 dB increase represents a perceived doubling of loudness, and an increase of 20 dB is about four times as loud. Sound confusing? Don't worry. All you need to remember is that 0 dB marks the threshold of our ability to sense sound, and as dBs increase, amplitude increases, and so does the perceived loudness of the soundwave. For example, a quiet room has a noise floor about 20 to 30 dB, while a normal conversation at the dinner table sits it at around 40 to 60 dB.
An average vacuum cleaner is about 80 dB, while front row at a rock concert gets up to around 120 dB. Beyond that, our threshold of physical pain starts at about 130 dB.
AuthorBrian Lee White
- Measuring frequency and amplitude
- Understanding the relationship between frequency and pitch
- Working with EQ controls such as bandwidth (Q) and gain
- Using graphic EQ
- Understanding the shelving and high-pass and low-pass filters
- Creating focus with EQ
- Creating complementary EQ curves
- Performing frequency bracketing with filters
- Automating EQ
- Using frequency analyzers
- Using harmonic generators to excite frequency content
Skill Level Intermediate
1. Understanding Frequency and Amplitude
2. Using Equalizers
3. Advanced EQ Topics
4. Additional EQ and Filtering Techniques
6. An Interview with the Author
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