Balanced input

Types of Balanced Inputs

The balanced input is a type of audio input that music production equipment and high-end audio systems use. It is a method used to connect audio sources (like musical instruments or microphones) to audio equipment (like recording systems or mixers). This is done so that any noise or interference that is picked up along the way is canceled out. This is done by using two cables to send the same audio signal, and then in the second one, the opposite of it is sent. In the end, the receiving end adds the two signals together, and this cancels out anything that was added along the way.

Some common types of balanced inputs are:

• XLR: It is a type of cable used to connect microphones and audio equipment. There are three pins in the XLR cable, one for the ground, one for the positive, and one for the negative. It is used by professionals because it is durable and has a good sound quality.
• TRS: This is a type of stereo cable that is used to connect audio sources like keyboards and headphones. It is used to connect unbalanced audio sources to balanced audio inputs. The full form of TRS is Tip, Ring, Sleeve. It has three parts: the tip, which is the left channel, the ring, which is the right channel, and the sleeve, which is the ground. The tip carries the original signal, the ring carries the inverted signal, and the sleeve is the ground.
• TRS: This is a type of cable that is used to connect guitars and other instruments to audio interfaces or amplifiers. It is a mono cable that has two conductors, a positive and a negative, and a ground. It is used to connect unbalanced audio sources to balanced inputs. The positive carries the original signal, the negative carries the inverted signal, and the ground is the ground.

Functions and features

A balanced input offers many useful features. In a studio, the input is used to record and monitor sound during production. The features include the following:

• Common mode rejection:

It removes noise that is present in both conductors. This is a unique function found in balanced inputs. To do this, the balanced input amplifier amplifies the difference between the two signals. The signals are in opposite polarity. By amplifying the difference, the noise is cancelled out.

• High input impedance:

The input impedance of the balanced XLR input is 10 MOhm. This is a very high impedance. It allows the input to take in many kinds of signals. No current is drawn from the source. Hence, delicate signals are not affected.

• Low output impedance:

The output impedance of the balanced input is 50 ohms. This is low enough to drive the cables and other equipment. The low impedance prevents noise from entering the signal when connecting different equipment.

• Gain control:

This is important for the preamp. The amp is the first device the signal from the source will meet. It may be too low to be heard or too high to sound good. The gain control will increase the signal level in the amp if it's too low. If the signal is too high, it will decrease the level.

• Clip indicator:

It warns the user that the signal level is too high. This will cause distortion in the recording. Most preamps have a red light that flickers when the signal is too high.

• Phantom power:

This is an important feature for microphones. Some mics need power to work. The balanced XLR input offers 48 volts of power to the mic. The power is not in the audio signal but is carried on the same wire as the audio signal.

Applications of balanced inputs

There are various applications for balanced inputs. Audio systems use balanced inputs to reduce noise, especially over long distances. It can be used in the following areas:

• Professional audio equipment: Most audio equipment used in recording studios, stages, and other professional settings use balanced inputs and outputs. Microphones, mixing consoles, and audio interfaces all have XLR or TRS connectors that support balanced connections.
• Live sound reinforcement: In live sound scenarios like concerts, balanced connections are vital for connecting instruments, microphones, and other gear to the main mixing console and speakers. This helps in ensuring a clean, noise-free signal throughout the audio chain, which is crucial for a high-quality live performance.
• Public address systems (PA systems): PA systems in large venues, schools, and offices also rely on balanced connections to transmit audio signals without interference or noise. The use of balanced inputs and outputs in amplifiers, mixers, and speakers helps in achieving clear and consistent audio broadcast to a large audience.
• Studio monitors: Balanced inputs are found on studio monitors and reference speakers to maintain audio quality. By using balanced connections between audio interfaces or mixers and the monitors, music producers and audio engineers can accurately monitor and mix their recordings without worrying about unwanted noise or interference.
• Installed sound systems: Sound systems installed in restaurants, retail stores, airports, and other commercial spaces utilize balanced connections to prevent audio degradation. Whether connecting background music sources, paging microphones, or distributed speakers, balanced inputs and outputs maintain a high signal integrity level in such environments.
• Instrumentation and test equipment: Balanced inputs are used in laboratories, factories, and other industrial settings where precision measurement and control are needed. Equipment such as oscilloscopes, signal generators, and data acquisition systems rely on balanced connections to ensure accurate and reliable data transfer, especially in electrically noisy environments.

How to choose balanced inputs

When selecting balanced input cables, one should consider the length of the cable. This is because it not only affects the overall sound quality but also the price of the cable. Short cables are less expensive than long cables, and it is better to buy a longer cable than a short one because the length can always be adjusted. A long cable allows for easier movement and positioning of the equipment.

The weight of the cables matters too, particularly in application settings where the cable is suspended. It is recommended to use a lighter cable in a stage box application to avoid putting excessive stress on the connectors and equipment. It is also important to consider the connectors of the cable. The connectors should be well soldered and made of strong material. They should be able to withstand constant plugging and unplugging. It is also important to consider the kind of shielding in the cable. Braided shielding is the most reliable, but spiral and foil shields also work well.

When choosing a balanced input cable, one should also look at the conductors. The size of the conductors should be put into consideration. The larger the conductor, the better the signal will be. The material of the conductor is also important. While copper is the most used material, other materials like silver-plated copper also work well. The arrangement of the conductors is important too. The closer the arrangement, the better the noise rejection.

The outer jacket of the cable should be made of heavy-duty material that can withstand constant movement. The jacket should also be flexible to make it easy to roll and unroll the cable. The temperature range and plug compatibility should be considered too. It is also good to choose a cable that is easy to repair. This can help save money in the long run. When choosing balanced input cables, one should also consider the price. That said, it is important to remember that not all expensive cables are of good quality. It is therefore important to strike a balance between price and quality to get value for money.

Q&A

Q1: What is a balanced input, and what are its benefits?

A1: Balanced inputs can reduce noise and distortion from long cable runs. They also help to reject interference from other devices. This improves the signal-to-noise ratio and provides clearer sound.

Q2: How far apart should balanced audio cables be placed?

A2: The cables for balanced audio should be kept as far apart as possible. This helps to reduce crosstalk and interference between them.

Q3: How many balanced audio cables can I run together?

A3: It is best to run only one set of balanced audio cables. Running multiple cables together can cause interference between them. This will reduce the benefits of using balanced cables.

Q4: What is the difference between a balanced and unbalanced audio cable?

A4: A balanced cable has two signal wires and a ground wire. An unbalanced cable has only one wire for the signal and one for the ground. The second signal wire in a balanced cable is the opposite of the first wire. This reduces noise and interference in the signal.

Q5: Can I use a balanced cable with an unbalanced input?

A5: Yes, an adapter can be used to connect a balanced cable to an unbalanced input or output. The adapter will connect the second signal wire to the ground wire. This allows the cable to work with unbalanced connections. The cable can still help to reduce noise and interference, even when used with an unbalanced device.