AUDIO SIGNALS AND CONNECTORS EXPLAINED
What is the difference between balanced and Unbalanced? What’s a line level signal? What’s Hi-Z and what Bitrate and Sample rate should I use? When new to recording and the world of professional audio, all these terms can be confusing. What do they mean and when should I use what? The “What Is” series will explain the basics of what you need to know, so you can record with confidence.
OTHER ENTRIES IN THE SERIES
Digital and Analog Signals:
• Line level
• Mic level
• Speaker level
• Balanced and Unbalanced
• High impedance
• Low impedance
• Sample rate
• Decibel scales
Inputs and Outputs and Connectors:
• Phantom Power
• Microphone inputs
• Line level inputs/outputs
• Instrument inputs
• Insert Channels
• S/PDIF inputs/outputs
• ADAT Inputs/outputs
• MIDI inputs/outputs
• Network Protocols
Analog audio signals, as well as digital audio signals, and how they relate to each other, is a topic that goes very deep, and I’m only going to skim the surface to give you a working knowledge on what the terms mean so you can make informed choices when working in your studio. With that said, let’s start with the Analog first.
At its core, an analog sound signal is an electrical representation of a sound wave. For example, When you speak into a microphone, the microphone generates an electrical signal in a wire. This signal can then be amplified and recorded or played back through a speaker.
An analog signal can be found in many forms, with different levels, impedances etc. Let’s look at the most common ones you find in the studio.
There are four main levels of signal strength that we use when working with audio. They are referred to as, from weak to strong:
- microphone level
- instrument level
- line level
- speaker level
These are all pretty self explanatory, but let’s look at them one by one anyway.
Microphone level is the weakest, and is what you would get straight out of your microphone. This level needs to be amplified before you can use it using a microphone preamplifier. This level, depending on the microphone used, is only a couple microvolts.
Instrument level is another weak signal produced by the pickups of electric guitars and basses. This also needs to be amplified. Normally by a guitar or bass amplifier. Like microphone level, we’re only dealing with a few microvolts
Line level is produced by digital pianos and synthesizers, the output of audio interfaces and recording consoles, as well as most other sources that’s not a microphone or an electric guitar or bass. It is the “working signal”. This is the level you record, the level expected by signal processors, etc. This level is usually around a volt or two.
As a side note, most professional equipment uses a standard of +4dBu balanced for line level, while consumer equipment uses a standard of -10dBV unbalanced. Some equipment have toggles to choose between these different levels, while others do not. Also note that dBu and dBv is not the same scale. The level difference isn’t 14dB as you might think. It’s actually closer to 11.79dB. The practical result of this is that you may feed too hot a signal from your pro interface to a consumer level processor or vice versa if you’re not careful. Also remember that these level differences aren’t tied to if the signal is balanced or not. We’ll touch more on balanced and unbalanced signals later.
Finally, speaker level is the signal produced by a guitar or PA amplifier. These signals can be incredibly powerful and should never be connected to anything other than a speaker.
The purpose of a speaker level signal is to move a speaker cone using
These levels can be hundreds of volts.
One thing to note though is that many studio monitors are what’s called active speakers. This means that they have their speaker amplified built in. As such, they expect a line level signal on their input.
Balanced and Unbalanced
The second thing you need to take note of, once you’re sure your output generates the signal expected by the input, is if the signal is balanced or not.
You may ask yourself, what is even the point of balanced cables? It’s just confusing to have two different kinds of audio cables. Why can’t everything just be one or the other? Let’s look at the difference and why you may want to use one or the other.
The short answer is balanced cables are more resistant to noise. An audio cable is not much different from an antenna, and it will generally pick up noise and interference from its surroundings. Balancing is a simple and clever way to practically eliminate this noise, and is is especially important when working with low level signals, such as between a microphone and the microphone amplifier, or during long cable runs, such as between a stage and mixing position during a live gig, as this noise increase with the length of the cable.
A balanced cable has three conductors, one positive signal wire, one negative signal wire, and a ground wire.
The trick of balancing is the existence of both the positive and the negative signals. Both are carrying mirror images of the same audio signal.
Unfortunately, while balanced connection is the most common in professional equipment, consumer and prosumer gear normally opt for unbalanced connections for the reasons of cost, and the cable runs are rarely long enough to justify the additional expense associated with making the outputs properly balanced.
Let’s look at a simple example of a typical signal chain to demonstrate these different signals.
In this example we have a speaker talking through a PA system.
The speaker uses their voice to produce sound waves in the air which is picked up by the microphone, which generates a weak mic level signal. This signal is transferred through the mic cable to a microphone preamplifier, which amplifies the signal to a line level signal. The level is now strong enough to be processed, and this is where we would normally apply equalisation and compression. Next we have a final amplification stage to speaker level, which is strong enough to physically move the drivers of a speaker to produce sound waves loud enough to be heard by the public.