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Characteristics of Sound - "Sealing the Envelope

From here we will continue to explore the rest of the characteristics of sound. Go ahead and take a second to explore harmonics and phase again, making sure you fully grasped those concepts. We cannot reiterate how important these two things are. Make sure to go over frequency and amplitude again in your head while you are doing this. If you need a refresher, you can revisit the first characteristics of sound.

Welcome back to the final segment of the characteristics of sound segment. If you are just landing here and have no idea what we are talking about you can check out Characteristics of Sound or if you have already read that one check out Characteristics of Sound: "Phase 2" to get filled in before you continue on. 

Going forward, we are going to explore three more concepts that play into the creation and the characteristics of soundwaves. We’ll be talking about envelopes, other periodic types of wave forms, and noise. These things are important in the capturing of sound and play roles in the creation of synths in synthesizers and “in the box” software on your digital audio workstation (DAW) or your external preamps, if you have any.


If you haven’t figured it out by now, we’re not talking about your standard paper envelope. Instead, Envelope is a description of how a sound changes over time and inevitably, how the listener distinguishes one instrument from another. Sounds come with their own envelope - pianos, snare drums, guitars - and these can be adjusted with the proper equipment (software or hardware) but we will go into that later. For now, we will talk about the four components that make up envelope: Attack, Decay, Sustain, and Release.

  • Attack - attack is the initial point of a note or sound envelope. This can be when a hammer hits a piano string, a drumstick hits a snare drum, a guitarist strums his guitar. This is the area that rises from silence to it’s peak volume
  • Decay - decay is when the sound or note stops peaking and begins to decline to a medium level
  • Sustain - sustain is the part of an envelope that is in constant level of decline
  • Release - release is the last point in an envelope where the sound returns back to silence.
  • Percussion instruments have very quick attacks meaning they will reach their note peak as soon as you strike the drum.
  • Here is an example of a piano key being pressed and it’s corresponding envelope:

These components are important to understand now, especially if you’ve already started to record live instruments. Take into consideration the envelope that each instrument has when it creates a pitch and move forward with that information accordingly to the best of your ability. If you are messing with an envelope already in your DAW, feel free to try each one independently. We recommend turning everything except attack and decay down to find a good starting point and resolve from there if you truly need to adjust these settings.

Other Periodic Waveform Types

Sound can come in other waveforms other than the traditional sine wave. Each waveform has its own characteristics in terms of sound and has unique applications. Some typical waveforms that you may come across are:

  • Square Waves - square waves are typically associated with digital audio and are usually described as hollow. Square waves contain the fundamental note plus the odd harmonics. These odd harmonics gradually decrease in amplitude the higher the frequency is.

  • Triangle Waves - typically used with synthesizers, triangle waves contain the fundamental note plus odd harmonics. Higher frequency harmonics are even lower in amplitude here, making higher frequencies less harsh.

  • Sawtooth Waves - Sawtooth waves contain both even and odd harmonic information as well as the fundamental note. Sawtooth waves sound harsh and clear and are typically used to replicate bowed string sounds on synthesizers. 

    As always, we will break down each of these waveshapes down a little more in a future article, but these are pretty good representations and explanations of the typical waveshapes you’ll run into if you’re not dealing with sine waves. This is important when working with synthesizers, whether their physical or digital. 


    Noise and Distortion

    After moving on from the other types of waveshapes you may run into out there getting your hands wet learning how to audio engineer, noise and distortion are the last big things we’ll talk about that you’ll run into pretty often. Noise can be classified as any unwanted sound that is non-repeating and extraneous. Noise can come from pretty much any source that isn’t the intended source (i.e. an instrument, a singer, etc.). 

    In order to figure out the quality of an audio sample, engineers use Signal - to - Noise ratio. This ratio is used to figure out the amount of desired audio compared to the amount of undesired audio. From that we can infer that more desired audio present means that your audio sample is higher quality. This SNR is put up as a ratio where signal power:noise power and is often expressed in dBs. 

    Distortion, on the other hand, is caused by setting your levels to high (hot) meaning your gain staging is too high, your levels are clipping, etc. This can also happen when you push your tubes too hard (vacuum tubes) or when your equipment can not handle the workload you’re giving it. This can happen with poorly built equipment with cheap electronics or old electronics. 

    When setting up your mix, whether it is going to be a live one or a recorded set, make sure you check your Headroom. Setting your levels to high can result in nasty distortion and spikes in sound that will ruin a take and are quite unpleasant to the listener. Checking headroom before recording or during a warmup is a good way to avoid this problem. All you have to do is set the levels you would like and listen to the output - if it’s distorted adjust the levels you just increased and listen again. If you have visual meters these will help you gauge how much you will need to adjust.

    Hopefully, you have a grasp on these concepts and why they are important. Feel free to move on at your own pace from here or follow the skill trees as the go in order. Don't hesitate to go back over the previous Characteristics of Sounds articles.



    --- Sources ---

    • Tim Dittmar, “Audio Engineering 101: A Beginner’s Guide to Audio Engineering”
    • As always, our past experiences and training