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Learn the difference between mic-level signal, instrument-level signal, line-level signal, and speaker-level signal.
Microphone, instrument, line and speaker level signals differ in terms of voltage levels. From weakest to strongest voltage level goes the mic level signal, the instrument level signal, the line level signal and then the speaker level signal. – Audio Signals (Blog)
The exact signal level depends on things like the volume of the audio source, so it makes the most sense to think of these different signal levels as weaker or stronger than one another, as opposed to trying to define specific voltage levels for each one. signal type. You get to learn these signals in top audio engineering colleges in India.
1
Line Level Signal
If you feed a mic or instrument level signal into a line input on a piece of hardware, you’ll end up with a very weak and, in some cases, almost inaudible sound. This is incredibly problematic when you run the signal through a device that is input-level dependent, like a compressor. If the input signal isn’t strong enough to drive the line input, the signal won’t breach the compressor’s threshold level, so it’s not going to apply compression.
Line level signal is often referred to as the “standard” audio signal level because most external hardware like EQs, reverbs, and delays are built to accept line level signals. Other devices that can accept line level signals include mixing consoles and audio interfaces.
In the same way that it’s possible to feed a device a signal that’s too weak, it’s just easy to feed a device a signal that’s too strong. For example, if a device is meant to accept a mic level signal or an instrument level signal, but you feed it a line level signal, you’ll overdrive the device, which can result in heavy distortion.
There are actually two common types of line voltage levels, which include -10 dBV and +4 dBu. The inputs and outputs on consumer electronics are usually designed to work optimally with -10 dBV line signals, while the inputs and outputs on audio gear are often designed to work optimally with +4 dBu line level signals, which are a bit stronger than -10 dBV signals.
If you are working exclusively with audio devices, most of them probably require a +4 dBu line level signal, but some audio devices may have a switch that allows you to switch the inputs between -10 dBV and +4 dBu mode. This allows you to use both consumer and professional audio equipment.
Connecting a -10 dBV output to a +4 dBu input will always increase the noise level. However, you’ll usually end up with a cleaner signal if you boost the gain in your audio equipment, as opposed to overdriving the outputs of your consumer equipment.
Routing signals in the opposite direction, from a +4 dBu output to a -10 dBV input, can overload the inputs on the consumer device. In this case, you’ll want to mute the output of your +4 dBu device.
Pieces of equipment that use these two line-level signal variants can be interconnected, but be sure to boost or attenuate the signal in your audio equipment to suit your consumer equipment. In general, you want to stick to using devices with +4 dBu line inputs and outputs whenever possible, as they provide more headroom than devices with -10 dBV.
2
Mic Level Signal
It’s clear that you often need to somehow boost mic level and instrument level signals to line level, but how do you do that?
A microphone preamplifier is designed to increase the level of microphone level signals that are typically produced by microphones. If you own an audio interface, there’s a good chance it has at least one mic preamp built into it, but stand-alone mic preamps also exist.
Basically, all mic preamps do the same thing, which is amplify the mic level signal to line level, but some mic preamps introduce a certain desirable character while others attempt to provide clarity. Various stand-alone preamps also include built-in EQs or compressors to provide additional functionality.
In some studios, you will see a preamp chassis that is designed for 500 series mic preamps. Recording engineers often own several of these small preamps, giving them the ability to apply different tonal qualities to their recordings depending on which preamp they choose to use.
When you’re recording with the preamps built into your audio interface, you’re left with one option. Although most audio interfaces include preamps that sound pretty darn good. Even preamps found in entry-level audio interfaces can produce professional-quality results.
You won’t hear too many people blaming a bad recording on their preamps, but an assortment of separate mic preamps provides a little more versatility and can make it a little easier to find the sound you’re looking for.
3
Instrument Level Signal
Electric guitars and basses produce high-impedance, unbalanced signals at the instrument level.
The first problem is that the pickups in these instruments produce a relatively high impedance signal, so you have to run them to an extremely high impedance input. Unfortunately, not all audio devices provide high-impedance inputs. When you feed a high-impedance signal into a low-impedance input, the highest frequency content is lost, which you probably don’t want.
The second problem is that the signal that the guitars and basses produce is unbalanced; this means that if you try to run the signal through roughly 25 feet of cables, you will introduce unwanted noise into the signal. Factors such as how well your cables are shielded determine the intensity of the noise. At some point, however, heavily shielded cables won’t cut it.
You need a device that will provide a high-impedance input and convert the incoming high-impedance, unbalanced signal to a low-impedance, balanced signal. Fortunately, that’s exactly what a direct injection box does – they’re also commonly called DI boxes. You plug an electric guitar or bass into the DI input jack and it creates a low-impedance microphone signal.
You can then use a balanced XLR cable to carry the signal a considerable distance without worrying about noise and process it just like any other mic-level signal. If you wanted to run it into a home mixer or PA, now you could.
There are passive and active DIs. Passive DIs isolate ground voltages and eliminate ground loops; they are great for heavy duty instruments and are also cheap and durable. For this reason, they are a very popular choice.
Active DIs include a preamp, while passive DIs do not. They can help manage long cables and increase the gain of weak signals. As they tend to provide more headroom than passive DIs, they are also suitable for instruments with active pickups. The downside to active DIs is that they require power, which can be a bit of an inconvenience, and they’re often a bit more expensive than passive DIs because they’re more complex devices internally.
Many DI boxes include pass-through in addition to the low-impedance microphone output. Passthrough passes the high-impedance input signal directly through the device to a separate output, allowing the signal to be routed to an amplifier on stage. The amplifiers have high-impedance inputs, so they unsurprisingly accept signals at the level of high-impedance instruments.
You can route the low-impedance mic-level signal that the DI box produces to the PA using balanced XLR cables, while simultaneously running the high-impedance high-pass signal into the amp.
When it comes to recording, this setup allows you to record a guitar signal without effects, while simultaneously recording a guitar signal going through pedal effects and an amp. If you want to record the amplifier, just set up a microphone in front of it. You then have the option to apply the processing to the unaffected guitar signal in the box using plugins, or if you prefer, you can mix the dry guitar signal with the processed guitar signal you recorded.
A DI box used to convert an instrument-level signal to a low-impedance microphone-level signal, while a high-impedance version of the input signal is fed to the pedalboard – via the DI box’s bandwidth.
You probably don’t need a DI box to record guitar at home unless you want to split the signal in the way I just mentioned. Most audio interfaces have a high-impedance input, which is often marked with the text “HI-Z”. If you plug an electric guitar or bass directly into the Hi-Z input on your audio interface, you don’t need a DI box. You can record your guitar directly into your digital audio workstation using the HI-Z input on your audio interface.
4
Speaker Level Signal
A speaker level signal is a signal that has been amplified using an amplifier. When you run a line signal into your studio monitors, the amplifiers built into the speakers boost the signal up to speaker level. Smaller speakers require fewer volts to produce sound waves, while larger speakers require more volts.
Figure 10: Line signal boosted to speaker level with an amplifier.
If you find a speaker level output on a piece of hardware like a power amplifier, be very careful. Connecting this output to a microphone, instrument or line input on a piece of equipment may damage it. Make sure you connect only the speaker level outputs to the speaker level inputs.
You’ll also want to make sure you make these connections using speaker cables. Speaker cables are unshielded and use strong wires. If you use the wrong type of cable, such as an instrument cable that is shielded and contains thin wires, you can melt the cable and damage your amplifier as well.
Most companies label their cables so it’s easy to tell what type of cable you’re dealing with. However, if you find yourself looking at a cable that isn’t labeled and you’re not 100% sure what type of cable it is, just unscrew the end of the cable and look inside.
An audio input interface like the Focusrite Scarlett 2i2 lets you record mic, instrument and line level signals. If you’re looking for a more robust recording solution, consider taking a look at Universal Audio’s Apollo x8 audio interface.
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