Describing Factors of Sound
Everything that touches the sound will influence it, and therefore affect the sound quality in one way or another. Here are the different traits that are relevant to speakers, amplifiers, microphones, and room acoustics.
1- eq response
2- transient response
3- level of precision/ resolution
1- eq response
A speaker, amplifier, microphone, or a room might boost or reduce certain frequencies. Sometimes, this is desirable, sometimes it is not. For instance, a subwoofer is not designed to have an even frequency response, it is designed to produce low frequencies louder than high frequencies. Some microphones seem to have a natural eq curve as well, such as ribbon microphones which tend to capture less high frequencies
2- transient response
This is how quickly sudden surges in sound are reproduced. It’s most noticeable with percussion instruments, such as a kick drum, or a snare drum which become very loud very suddenly. Sometimes, a piece of gear is not capable of the sudden change, and requires a ramp up time. An example is a large subwoofer speaker trying to replicate the snappy thump of a kick drum. It will be sluggish, not snappy. Here’s a screenshot of a wave from a kick drum, and the same sound played from a large subwoofer and recorded. As you can see, the subwoofer is not capable of the sudden start and stop.
3- level of precision/resolution
This is how precisely the wave is reproduced, and is especially noticeable in the high frequencies. Higher frequencies have smaller waves, and so eventually the waves are so small that they cannot be produced. For instance, a subwoofer is just too big and heavy to produce the tiny sound waves of high frequencies.
Additional unwanted sounds being added. This can be white noise, a car driving by, or buzzing. Sometimes it’s noticeable, sometimes it’s so slight that it is not noticeable. What’s common, is in amplifiers, a level of white noise that’s added to the signal, that fluctuates along with the sound volume. For instance, in this example, I have an original recording of me speaking, and I have it re-recorded. While you can tell hat the re-recorded one sounds different, can you hear the noise? Probably not. But when I remove the original recording from the re-recorded track, then you only hear the noise, and you can hear it fluctuate with the volume changes.
Technically, distortion is any change from the original sound, what I will be talking about here is specifically a type of distortion called clip distortion. This is when the volume of sound is too high, the piece of equipment is simply not capable of fully reproducing the sound. So the top and bottom of the wave are clipped off, hence the name clip distortion. An example is a subwoofer with limited in and out excursion. In an amplifier, the voltage determines the maximum amplitude the circuit can handle. In lesson 1.4 how Sound flows as electricity, as well as 1.6.2 about distortion explain this in more detail. What’s important for this lesson is that it has a negative effect on the sound quality, with the exception of when it’s done intentionally to get that sound, such as in guitar amplifiers.
7- phase. 1.3.2
Sound is a wave, and if it is duplicated, and summed, or added to itself, if the copied wave does not perfectly match the timing of the original, it will be out of phase, and this will change the sound. Examples are when a microphone is close to a wall, it will pick up the instrument it is recording, but then pick it up again a few milliseconds later because part of the sound bounces off the wall, and then arrives into microphone. It can also be a problem if you have bass coming from your main speakers, and you also have a subwoofer placed a little farther away. The speakers and subwoofer are both producing the same sound at the same time, but their sound doesn’t reach you, the listener, at the same time, and it is therefore out of phase. As an audio engineer, you are manipulating sound, and understanding phase is a crucial for many aspects of the recording and sound design process, and that’s why there’s an entire lesson on it, 1.3.2, phase.