Selection of audio equipment transmission cables

The signal transmission between analog or digital devices in the audio equipment system must be interconnected by cables. Regardless of the system format or application format of the system equipment, the cables used are crucial. Often in practical work, sometimes the communication characteristics of cables are overlooked in a certain link, and the various transmission characteristics of cables for different uses and the plug characteristics for connecting different devices. No matter how good the audio equipment is, without selecting audio cables and connectors that achieve reasonable communication characteristics matching, the best technical performance cannot be achieved, leading to unimaginable adverse consequences. Therefore, based on the professional theory learned and many years of audio technology work practice, this article discusses the selection of audio equipment transmission cables for reference by relevant audio technology workers.

1. Digital Audio Cable

Commonly used digital audio cables can use the same connectors as analog audio, such as Cannon XLR, RCA phono, BNC, etc. Using analog cables instead of digital cables can still transmit signals, but it may affect transmission quality.

Analog cables and the output impedance of digital equipment have strict requirements for cable impedance. Regardless of the length of the analog cable, the impedance at various points on the cable is 600Ω. Analog devices with input and output impedance less than 600Ω when matched will not affect the sound quality of analog audio. This is different for digital audio devices. Digital audio signals are high-frequency pulse data streams. In order to accurately transmit signals, the cable must match the sending and receiving devices. The cable impedance from end to end must maintain a consistent standard. For example, digital AES/EBU requires standard cables for I/O format interface connections, and coaxial cables or twisted pair cables should be selected as transmission media. The characteristic impedance of twisted pair cables is 110Ω. Otherwise, damage to the transmitted digital signal may prevent the system from working properly.

If analog device cables are used instead of digital cables on digital devices, the characteristic impedance will not match. Since digital signals have very high frequencies, having the current skin effect deeper on the conductor leads to better transmission. When the impedance does not match, the skin effect is shallower, resulting in poorer transmission. This is because most currents in the cable cause reflections, generating standing waves that consume signal energy and distort the waveform of digital pulse signals. When the cable impedance does not match, distributed capacitance, distributed inductance, and resistance in the cable can directly affect the frequency response of the signal, impacting the rise and fall times of the pulse. This mismatch can lead to errors in interpreting digital signals at the receiving end. If there is a deviation in rise and fall times, it can cause long jitter, reducing audio quality and even generating noise that degrades sound quality.

When recording and producing various programs, audio cables are needed for assembling audio system equipment. Apart from digital consoles, there are many analog peripherals such as microphones, equalizers, delays, effects processors, synthesizers, D/A converters, audio processors, digital recording and playback devices, monitor speakers, etc. It is often assumed that simply connecting them is enough, neglecting quality transmission standards. If the technical specifications of the equipment used are not high, the deficiencies in the cable may not be apparent. Matching impedance cables become an important part of meeting audio standards in recording studios where equipment specifications are at the entry level. To achieve this, transmission cables that match the equipment must be used, and concurrently, the input and output levels of the equipment must be properly matched.

2. Analog Audio Cables

Analog audio cables can be roughly divided into microphone cables, transmission line cables, and speaker cables. Audio cables come in single-core, twin-core, and three-core varieties. The core is the conductor for audio signals; the outer layer of the conductor is a shield made of braided mesh and protective layer composite metal wire, which shields against external electromagnetic interference and can also be used as a signal ground. The outermost layer of the shield is covered with non-conductive plastic or rubber, which serves to protect the shielded wire against tensile forces and corrosion. The outermost layer can protect the internal layers, ensuring the longevity of the cable. Audio cables also consider skin effect. Copper wire surface plated with silver or tin is commonly used as a conductor, as it is cost-effective, has good conductivity, and is easy to move.

Analog audio cables make typical use of several connector forms. Microphones usually use Cannon connectors (XLR) or (RTS) 6.25 three-core (1/4 inch), and unbalanced connections often use (RS) 6.25 two-core or RCA phono connectors. Speaker cables commonly use large-diameter multi-strand copper wires, sometimes with banana plugs or other self-locking connectors. It is essential to maintain the tightest connection when pairing plugs and sockets. The appearance of cables used in analog and digital devices also differs slightly, and with careful observation, they can be easily distinguished. It is crucial not to mix them up or use them incorrectly, as this determines the quality and performance of the audio system equipment, which is a significant aspect of audio equipment technology work.