Signal Transmission in Audio Systems: Key Considerations
Professional audio systems consist of numerous functional devices. After designing the system based on requirements and selecting equipment, these discrete devices must be interconnected to form a complete system fulfilling the design goals. For fixed installations, devices are mounted in racks, and all system wiring is permanently installed following standards/specifications. For mobile systems (concerts, outdoor events), secure temporary fixation of equipment and cables is crucial for safety.
Audio system connection and installation involve engineering aspects: control room design/construction, cable conduit work, system power supply, etc. Here, we discuss key considerations for signal transmission in audio systems.
1. Impedance Matching
The signal input port acts as the load for the signal output port. The required impedance matching range depends on the output device's design specifications. For optimal audio signal transmission, the input impedance must match the source output's load requirements. Otherwise, device operation is affected, causing output signal distortion—potentially damaging the source.
Theoretically, maximum signal transfer efficiency occurs when output impedance equals load impedance. If output impedance exceeds load impedance, significant signal energy is lost in the output circuit—detrimental to transmission. Hence, audio devices are typically designed with input impedance > output impedance.
Generally, connections work if load impedance > signal output impedance. However, input impedance shouldn't be too high (reduces cable noise immunity) or too low (degrades frequency response).
2. Signal Transmission Level
System connection aims for signal transfer. Optimal transmission requires the source output level ≥ input sensitivity. Otherwise, Signal-to-Noise Ratio (SNR) deteriorates. Professional audio line input/output circuits are usually set to 0dB gain—neither amplifying nor attenuating signals to maintain level during transmission. This ensures level control units have a reliable reference.
Match output/input levels during connection. Mismatch risks clipping distortion or insufficient drive, degrading overall system SNR. Audio devices (mixers, processors, amps) typically connect at line level. Common standards: +4dBu (1.228V) or 0dBV (0.775V). Uniform levels simplify setup.
Note: Some processors (especially effects units) have interface level switches (+4dB, -10dB, -20dB) for instrument/pro-audio compatibility. Set to +4dB for PA systems.
3. Weak Signal Connection Methods
Professional audio I/O ports include unbalanced, transformer-balanced, differential-balanced. Balanced-to-balanced and unbalanced-to-unbalanced connections work directly. For demanding applications, balanced/unbalanced connections require dedicated converters: passive transformer, half-voltage, or active differential amplifier types.
In less critical situations, unbalanced outputs can connect directly to balanced inputs: Connect balanced hot (+) to unbalanced signal, balanced cold (-) to unbalanced ground, balanced ground to cable shield.
Except for amp-to-speaker power transmission, use balanced connections for signal transmission whenever possible to improve noise immunity and SNR. Professional equipment generally provides balanced I/O.
Balanced transmission uses 3 wires: 2-core shielded cable. The shield is ground; inner cores carry hot (+) and cold (-) signals. Signal currents in the cores are equal but opposite. Thus, induced electromagnetic interference subtracts/cancels at the input.
Professional systems sometimes incorporate consumer sources (unbalanced output). Instruments like electric guitars, basses, keyboards, synths also use unbalanced outputs. Therefore, unbalanced connections are unavoidable. Key points: Keep unbalanced cable runs short, especially at low levels. Place an amplifier near the unbalanced source to boost level and convert to balanced for long runs. Transformers can also convert to balanced.
Audio system connection and installation involve engineering aspects: control room design/construction, cable conduit work, system power supply, etc. Here, we discuss key considerations for signal transmission in audio systems.
1. Impedance Matching
The signal input port acts as the load for the signal output port. The required impedance matching range depends on the output device's design specifications. For optimal audio signal transmission, the input impedance must match the source output's load requirements. Otherwise, device operation is affected, causing output signal distortion—potentially damaging the source.
Theoretically, maximum signal transfer efficiency occurs when output impedance equals load impedance. If output impedance exceeds load impedance, significant signal energy is lost in the output circuit—detrimental to transmission. Hence, audio devices are typically designed with input impedance > output impedance.
Generally, connections work if load impedance > signal output impedance. However, input impedance shouldn't be too high (reduces cable noise immunity) or too low (degrades frequency response).
2. Signal Transmission Level
System connection aims for signal transfer. Optimal transmission requires the source output level ≥ input sensitivity. Otherwise, Signal-to-Noise Ratio (SNR) deteriorates. Professional audio line input/output circuits are usually set to 0dB gain—neither amplifying nor attenuating signals to maintain level during transmission. This ensures level control units have a reliable reference.
Match output/input levels during connection. Mismatch risks clipping distortion or insufficient drive, degrading overall system SNR. Audio devices (mixers, processors, amps) typically connect at line level. Common standards: +4dBu (1.228V) or 0dBV (0.775V). Uniform levels simplify setup.
Note: Some processors (especially effects units) have interface level switches (+4dB, -10dB, -20dB) for instrument/pro-audio compatibility. Set to +4dB for PA systems.
3. Weak Signal Connection Methods
Professional audio I/O ports include unbalanced, transformer-balanced, differential-balanced. Balanced-to-balanced and unbalanced-to-unbalanced connections work directly. For demanding applications, balanced/unbalanced connections require dedicated converters: passive transformer, half-voltage, or active differential amplifier types.
In less critical situations, unbalanced outputs can connect directly to balanced inputs: Connect balanced hot (+) to unbalanced signal, balanced cold (-) to unbalanced ground, balanced ground to cable shield.
Except for amp-to-speaker power transmission, use balanced connections for signal transmission whenever possible to improve noise immunity and SNR. Professional equipment generally provides balanced I/O.
Balanced transmission uses 3 wires: 2-core shielded cable. The shield is ground; inner cores carry hot (+) and cold (-) signals. Signal currents in the cores are equal but opposite. Thus, induced electromagnetic interference subtracts/cancels at the input.
Professional systems sometimes incorporate consumer sources (unbalanced output). Instruments like electric guitars, basses, keyboards, synths also use unbalanced outputs. Therefore, unbalanced connections are unavoidable. Key points: Keep unbalanced cable runs short, especially at low levels. Place an amplifier near the unbalanced source to boost level and convert to balanced for long runs. Transformers can also convert to balanced.