Two types of Line Levels: PRO level and Consumer Level
OK so you now clearly understood microphone, line and instrument levels. So if you see input requiring line level signals, then you should feed that with a line level input right? Not so fast; this is where beginners in home recording can still commit some mistakes. There are two types of line levels that you should know which are very important.
First, there is a “consumer line level”. This is defined to have a line level equal to -10dBV. dBV is a voltage measurement relative to 1 volt. Converting this to equivalent voltage level that you can understand and relate:
dBV = 20log (Vlevel)
-10 = 20log (Vlevel), solving for Vlevel which is the consumer line level voltage:
Consumer line level voltage = 0.316 volts, this voltage is in RMS measurement.
Second, there is a “pro recording line level”. This is equivalent to a voltage level of +4dBU. dBU is a voltage measurement relative to 0.775 volt. Converting +4dBU to equivalent voltage level:
+4=20log (Vlevel/0.775), solving for Vlevel which is the pro- line level voltage
Pro line level voltage = 1.23 volts
So you have seen that there is a big difference between a consumer level and pro line level voltages. Consumer line level voltages are commonly seen in non-professional audio recording equipment such as hi-fi equipment and CD players. Pro line level voltages are used by professional recording gears like recording pre-amps, etc.
Best practices when dealing with line, instrument & microphone levels
Below are some of the best practices you can implement in your home recording to get the best recording quality when working with any types of voltage levels.
1.) You will get a poor recording signal if you plug -10dBV equipment (a consumer line level) into an input requiring +4BU (pro recording equipment). To avoid this mistake, make sure you understanding the output and required input levels for signal compatibility. You can often get this information from the manual or ask the equipment manufacturer.
2.) Do not ever plug microphone directly to line inputs. A line input assumes that the signals are already amplified. As a result, you will get a noisy output from the microphone because it’s not pre-amplified.
3.) Use balanced XLR inputs in the mixer for plugging the microphone. This will ensure that the microphone signal will go to the pre-amplification stage. For example this is the screenshot of the Behringer Xenyx manual:
Image credits: Behringer Xenyx Manual
4.) Understand what type of line input is required (is it consumer level or pro-level inputs). Again refer to the equipment manual for the specifications.
5.) Guitars with active pickups can be plugged directly into line level inputs provided they have an output voltage of 1.75volts (which is greater than the pro-line level required voltage of 1.23 volts). When in doubt, contact the guitar pickup manufacturer and verify.
6.) Guitars and bass with passive guitar pickups cannot be plugged directly into a pro-line level input (such as in the mixer) because they have output voltages less than the required level. You need to plug the guitar input into the pre-amp input of your mixer or audio recording interface.
7.) A good way to assess whether you are connecting the right input-output combination of your gears is to look at the level meter of audio interface, in DAW or in the hardware mixer. For example, not using XLR input for connecting dynamic microphone to the mixer and plugging it directly to the line input will get a very low recording signal level (because it is not being passed into pre-amplification stage) with much hiss and noise (as you increase the trim or main output volume). In this case, the level meters will barely move and the signal is not good.
Content last updated on August 7, 2012