Next lesson playing in 5 seconds

Cancel
  • Overview
  • Transcript

2.2 Signal-to-Noise Ratio

Signal-to-noise ratio is one of the most important aspects of audio recording. In music recording, a bit of noise can often be masked by other instruments, but with a single voice you are much more exposed, and getting a good signal-to-noise ratio is critical.

2.2 Signal-to-Noise Ratio

Signal to noise ratio is one of the most important aspects of audio recording. In music recording a bit of noise can often be masked by other instruments, but with a single voice, you are much more exposed and getting a good signal to noise ratio is critical. Signal to noise ratio, often abbreviated as SNR or S/N, compares the level of a desired signal to the level of background noise. Background noise can literally be noise in the background. But it can also be noise generated by your microphone, noise from the preamp, noise generated in the electronics in the analogue to digital conversion itself. Or external environmental noise, like an HVAC system. Noise is anything that's not the signal that you're trying to record. Getting more signal to noise means a cleaner, clearer sounding recording, and is a fundamental concept in recording. In digital audio, zero dBFS or zero decibels full scale is a sign to the maximum possible digital level. All levels that fall below this maximum will be given a negative value. For example, negative ten decibels. Zero dBFS is also where digital clipping occurs. When the value of a signal is larger than the zero dBFS maximum, the wave form gets clipped, or squared off and can sound nasty. I'm gonna go over this a little bit more later when we talk about setting levels but for now all you need to understand is that you cannot go above zero dBFS. So, how do you get a good signal to noise ratio? Well to start, you want to record in a quiet environment. Sometimes, this will mean that you will have to record when people and traffic are less active. Depending on your area, that could be early in the morning, late at night or in the middle of the day. You want to make sure that you are away from large appliances that might be running and making noise. Like refrigerators, dish washers, laundry machines and HVAC systems. You also want to keep away from smaller devices that produce noise like computers and external hard drives. The other important element to getting a good signal to noise ratio is getting the microphone close to the sound source. The mic should be about eight inches away from your mouth. As the mic gets further away the direct sound of your voice is reduced and the reflected sound of your voice bouncing around the room and the ambient noises that are in your space will be increased. This is a recording of the AKG C3000B from about eight inches away. This is a recording of the AKG C3000B Large Diaphragm Condenser microphone from about 12 inches away. This is a recording of the AKG C3000B Large Diaphragm Condenser Microphone from about 24 inches away. This is a recording of the AKG C3000B Large Diaphragm Condenser Microphone from about 48 inches away. Getting the microphone close to your mouth is really the most important thing. This is especially true with voiceovers. If you wanna capture the dynamic range and subtle nuances of the voice, getting the mic in close is the way to do it. That said, you do not want to get the microphone a lot closer than eight inches, because you will start to get some nasty side effects like air bursts and mouth clicks. Getting a good signal to noise also means setting appropriate levels on your preamp. If you have isolated yourself from external noise sources as best you can, there will still be noise in your recording. This comes from the AD conversion, the preamp and even the microphone. And this is called the noise floor. The noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within your system. If you set he recording level of your microphone too low the level of your voice will be sitting much to the noise floor of your recording system. When you bring up the level in post production you will be bringing up all that noise as well. What you'd wanna do instead is record with a signal that's far above the noise floor, without clipping. This is done by turning up the gain on the preamp so you have a strong signal, usually with peaks around negative ten decibels. As long as you are using a decent microphone preamp and have the microphone close, this will get the signal well above the noise floor, and you will get a very good signal to noise ratio. If you were using a microphone that had a lower output and a lower quality preamp, you would be pushing the preamp to a point where it will start generating audible noise. And this is also something that you don't want. This means that you have to have decent equipment, a relatively quiet environment and good microphone placement in order to get maximum signal to noise performance. You're going to learn more about the specific things coming up later in the course. In the next few lessons, I will be going into more detail about the gear used for recording voice overs, starting with the next lesson on computers and software.

Back to the top