Audio electronics is an industry that refers to circuit design that converts sound into electrical signals or electrical signals back into sound. Together, several circuits form an audio system.
An audio system has several functions and can typically:
- Receive audio signals (through a microphone)
- Record and save audio
- Transmit audio (via wired or wireless communication channels)
- Play audio signals (through speakers)
Audio circuits are those that process the sound signal in the form of electrical signals. These circuits can also manipulate electrical (audio) signals by filtering, mixing, amplifying, or reproducing the sound of the signals. Such processes are executed by different circuits or devices.
In this series, we will design three audio circuits as follows:
1. Audio crossover
2. Audio equalizer
3. Audio Mixer
Crossover and audio equalizer are two different types of audio filters, which are one of the basic building blocks of an audio system.
Typical audio system
Before discussing the basic components of an audio system, it is important to understand the physics behind sound. After all, the circuits designed for this project technically manipulate electrical signals to represent audio.
Sound like waves
A sound is a form of energy, just as heat, light and electricity are forms of energy. Sounds are produced, propagated and detected as vibrations. As such, it is concluded that for the production of sound waves a source is necessary to produce the vibration. Once produced, a vibration will disturb any particles that are present in the surrounding environment – and these particles will further disturb any others that are nearby.
It may be easier to visualize these vibrations as a wave. An analog wave is produced by the compression and rarefaction of particles. Technically, it is this compression and rarefaction that creates a pressure wave, which is sound. In other words, a sound is a pressure wave characterized by waveform-like properties of amplitude, frequency, and time period.
Sounds like a pressure wave
The sense of hearing is the ability to detect and recognize sound waves. The perception of sound by humans and animals is determined by the range of frequencies to which they are tuned. Every living creature has a different sound perception. For example, humans can hear sound frequencies in the range of 20 Hz to 20 kHz.
Sound pressure level
The physical properties of sound are quantified by a sound pressure level. It is the measurement of sound pressure in reference to the minimum level that humans can hear. Sound pressure is expressed in micropascals (µPa) or pascals (Pa), while sound pressure level is expressed in decibels (dB).
Sound pressure
Sound pressure is the force (in Newtons) on a surface area (m2) perpendicular to the direction of the sound. The unit of sound pressure is N/m2 or Pa (pascal). The lowest sound pressure audible by humans is 20 µPa and the maximum sound pressure perceived by humans (which is also called pain threshold) is 20 Pa.
The sound pressure level is generally expressed in Db and is calculated as follows:
Lp = 10log(P2/P2ref)
Where…
Lp= sound pressure level
P = sound pressure (Pa)
Pref = reference sound pressure, 20 micro Pa
The reception of sound waves by human ears
Characteristics of a sound wave
A sound wave has three basic properties:
1. Tom
2. Volume
3. Tom
1. Argument
Pitch is the individual perception of sound, which cannot be measured by any mathematical equation. Instead, it is determined by how quickly a sound wave vibrates air particles. It is expressed as the frequency of a sound wave and represented by the compression and rarefaction of air particles. Therefore, the frequency of a pressure wave physically represents how quickly the compression and rarefaction of these particles occurs. are happening.
Although a tone is typically described by the frequency of a specific sound wave, it is not directly related to frequency. Frequency is simply the physical property of audio vibration used to determine the pitch of a sound.
The frequency of a wave can be determined by this equation:
Frequency = 1/Time
The frequency and time period of a wave have an inverse relationship. For example, as the time period increases, the frequency decreases and vice versa.
This means that the frequency of the sound wave indirectly expresses its height. Frequency is the number of waves in a given period of time. The period can be one second, one minute or one hour.
The standard frequency unit (ISI) is Hertz (Hz). Hertz is defined as the number of cycles per second. If there are 50 cycles in a second, for example, the frequency will be 50 Hz.
As humans can hear sounds from 20 Hz to 20 kHz, this frequency spectrum is divided into different frequency bands:
- Sub-bass: 20 to 60 Hz
- Bass: 60 to 250Hz
- Mid-low: 250 to 500Hz
- Mid range: 500 to 2 kHz
- Upper mid range: 2 to 4 kHz
- Presence: 4 to 6 kHz
- Brightness: 6 to 20 kHz
A high frequency wave has a higher pitch and a low frequency wave has a lower pitch. Consider the sound of birds chirping (high pitch) compared to the sound of a dog barking (low pitch).
The sound frequency of a tone
2. Volume
Loudness is the auditory sensation that refers to the order of a sound wave from low to high. Loudness is a property of sound waves and is related to their amplitude. The greater the amplitude, the louder the sound and vice versa.
The amplitude of a sound wave is defined by the vibration of the source. The source transfers energy to a medium through vibration. A greater energetic vibration generates a greater amplitude.
Loudness represented by the amplitude of a sound wave
For humans, the intensity of a sound also depends on the sensitivity of their ears. Because humans are sensitive to certain frequencies, loudness depends on the amplitude of the sound wave and the frequency within a perceived audio perception range.
The energy of a sound wave is proportional to the square of the amplitude. Thus, the greater the amplitude, the louder the sound and the more energy it carries.
Loudness representation based on sound wave amplitudes
3. Quality
A pure tone is sound generated by just one frequency. In a sound wave, there are several tones or notes of frequency, but the fundamental note (fo) has the highest amplitude, so it can be heard easily. The fundamental note is the frequency at which an entire wave vibrates.
Frequency notes, which are perfect integer multiples of a fundamental note, are called overtones or harmonics. The sound wave is a combination of fundamental notes and harmonics.
The presence of overtones or harmonics distorts the sound and its perception, and this is called harmonic distortion. The fundamental note and harmonics have different amplitudes and energy levels. The smaller the amplitude of the harmonics and the lower the energy of all the harmonics combined, the higher the quality of the sound.
Therefore, the amplitude or energy of harmonic frequencies — such as 2fo, 3fo, 4fo, etc. — compared to the energy of the fundamental frequency, it determines the quality of the sound wave.
In the next tutorial, we will cover acoustic waves, which are a type of sound wave.