Lesson 7.2 - Working with Audio

In real life, sounds are emitted by a source, move through the air, and are heard by a listener. A listener is able to discern the sound’s location, direction of travel, velocity, distance, loudness, and pitch. The surrounding environment can dampen or reflect a sound and affect the way it’s perceived. The sound of a dog barking, for instance, is very different in a semi-enclosed alley versus an open-air stadium. In Unity, we can apply properties to sounds to recreate these types of scenarios.

When working with sound design in Unity, it’s best to have already recorded and edited your sound files in an external audio editor to make sure their levels are consistent and normalized. Additionally, you should import and save your audio files in the project’s Assets folder. For our example project, audio files are included in a folder named SFX, saved inside the project’s Assets folder.

1. Select the Background_music_loop audio file in the Assets folder to preview its properties in the Inspector. Click Play to preview the sound (Figure 01).

Figure 01: Listening to an audio file in the Inspector

2. Create an Empty GameObject in the Hierarchy window. Name it SFX and zero the X, Y, and Z Position coordinates. Create an Audio Source GameObject by selecting GameObject > Audio > Audio Source from the top menu drop-down (Figure 02).

Figure 02: Adding a new Audio Source GameObject

3. Parent the Audio Source within the SFX Hierarchy and rename it Background_Music (Figure 03).

Figure 03: The SFX Hierarchy, containing the Background_Music GameObject.

4. An Audio Source can also be added onto other GameObjects as a component. You can do this by selecting Add Component in the Inspector and searching for Audio Source (Figure 04).

Figure 04: The Audio Source component

5. With the Background_Music GameObject selected in the Hierarchy, link an audio file into the AudioClip field in the Inspector by first selecting the Object Loader Circle button next to the AudioClip property in the Inspector, and then selecting the Background_music_loop audio file (Figure 05). (Alternatively, select the audio file in the Project window and drag and drop it into the AudioClip field.)

Figure 05: The audio file applied to the AudioClip field in the Inspector

6. Enter Play Mode to preview the audio now in your Scene. You will be able to hear the music immediately if Play On Awake is enabled. You can also loop the sound file if Loop is enabled (Figure 06).

Figure 06: Play On Awake and Loop enabled

The Unity Audio Mixer gives you further flexibility to mix various audio sources. You can use the Mixer to master your audio, route audio channels, and add effects.

1. Select Window > Audio > Audio Mixer (Figure 07).

Figure 07: The Audio Mixer window

2. Beneath Mixers, select NewAudioMixer (Audio Listener) - Inactive to open up the Master side panel (Figure 08).

Figure 08: The NewAudioMixer’s Master audio levels meter

3. To send audio to the Mixer, you must first select the Audio Source GameObject in the Hierarchy and click the Output’s Object Loader Circle (Figure 09). Next, set the AudioMixer to Master in the AudioMixerGroup window (Figure 10).

Figure 09: The Audio Source GameObject’s Output field

Figure 10: Setting the AudioMixer to Master

4. Now, when you enter Play Mode, you’ll be able to preview the audio signal through the Audio Mixer (Figure 11).

Figure 11: Previewing the audio through the Mixer

Enhancing audio is possible through the Audio Mixer. Normalize, for example, keeps an audio signal’s levels more consistent. You would apply this effect if your audio source had varying volume levels that you wanted to even out. Or, you could use a Flange effect to simulate an acoustic environment where a listener is traveling out of an enclosed space into the open. You might also want more bass in your source audio, in which case you would use ParamEQ to adjust the audio equalizer. You can add these effects, as well as others, in the Audio Mixer window. Let’s add the ParamEQ effect now.

1. Select Add in the Audio Mixer window and then select ParamEQ from the drop-down (Figure 12).

Figure 12: Adding an effect in the Mixer

2. With the ParamEQ, you can start to make adjustments in the Inspector window (Figure 13).

Figure 13: The Parametric Equalizer in the Inspector

3. Select at a location on the graph by clicking and holding the mouse and dragging a curve upward to enhance a specific frequency range. Drag the slider for Center freq to adjust the curve left and right for a lower or higher frequency. Adjust the Octave range slider to narrow or widen the range of the curve. Adjust the Frequency gain slider to raise or lower the curve. Practice matching your curve to the example below, in which the lower bass frequencies are enhanced (Figure 14).

Figure 14: Adjusting the ParamEQ curve to enhance bass

4. Enter Play Mode to play back your audio track. To make adjustments to the audio effects in real time, first enter Play Mode and then select the Edit in Play Mode button in the Audio Mixer window, (Figure 15). While the audio is playing, make adjustments to the effect in the Inspector window. Try not to amplify the bass too much for the Background_Music audio source.

Figure 15: With Edit in Play Mode selected, you can preview audio adjustments in real time.

5. Delete any unnecessary or overused effects by right-clicking the effect and selecting Remove This Effect.

You can also adjust audio in the Inspector. The Reverb sound effect, for example, adds a level of depth to an audio source, giving it a spatial quality.

1. With the Background_Music GameObject selected in the Hierarchy, click Add Component in the Inspector, type in “audio,” and select Audio Reverb Filter (Figure 16).

Figure 16: Adding an Audio Reverb Filter component

2. In the Inspector’s Audio Source component, drag the slider for Spatial Blend from 2D to halfway through, or enter a value of 0.5 to enable and mix the 3D sound environment. Next, increase the Reverb Zone Mix slider to 1, such that we will be able to hear the Reverb settings when they are changed (Figure 17).

Figure 17: Adjusting the Spatial Blend and Reverb Zone Mix values

3. Now we’re able to preview the Reverb effect. Enter Play Mode and select the Reverb Preset field labelled User to open up a list of options (Figure 18).

Figure 18: The Reverb Preset options

4. Select any of the presets to preview its 3D spatial effect. You might not readily notice the difference between subtle Reverb Presets like Livingroom or Stoneroom. Experiment with changing the Reverb Presets to more dramatic options, like Cave or Concerthall. Finally, select Alley for an effect that resembles sound being emitted within a semi-enclosed 3D space.

The Unity Editor will not store any of the changed values in Play Mode. When you stop Play, the settings will revert back to their original state. Set the values after Play Mode has stopped if you want them saved.

Hint: When previewing subtle effects, it’s helpful to toggle the Bypass Reverb Zones checkbox in the Audio Source component (Figure 19).

Figure 19: Selecting the Bypass Reverb Zones to turn an effect on and off

5. Additional audio effects are available as separate components. If you’re going for a more rhythmic sound, add echo, which produces a stylistically unique effect. Click Add Component in the Inspector, search by typing “audio,” and then select Audio Echo Filter (Figure 20).

Figure 20: Adding an Audio Echo Filter

6. Experiment applying the Echo Filter values while in Play Mode to fine-tune the effect in real time (Figure 21).

Figure 21: The default settings for the Audio Echo Filter

When working with sound, certain effects can be carefully balanced and fine-tuned. As a general best practice, avoid maxing out, overusing, or exaggerating any sound effect unless it’s intentional. The audio effects won’t necessarily improve the quality of our Background_Music track; they’re merely illustrated here to show examples of applying sound effects to an audio source.

Just as we’ve used Timeline to add lights, cameras, and visual effects, we’ll use the same principles to add audio to our Scene. With Timeline, we can enable audio to play during a designated interval, or begin playing at a specific time in the animation.

1. In the Timeline window, select + to create a New Track Group and name it SFX Group. Then, select + again in the newly created SFX Group to add a New Audio Track (Figure 22).

Figure 22: Creating a new Audio Track for the Track Group

2. With the Audio Track highlighted, select its menu options button and then select Add From Audio Clip (Figure 23).

Figure 23: Selecting Add From Audio Clip

3. Select the Background Music audio file from the Audio Clip window (Figure 24).

Figure 24: Selecting the Background Music audio file

The Audio Track is now displayed in the Timeline. You can position it, as well as trim the beginning or end as you’d do when working in the Timeline (Figure 25).

Figure 25: Selecting the Background Music audio file

4. Because the Background_Music GameObject audio in the Hierarchy will play over the newly created track in the Timeline, we’ll need to turn off its Play On Awake setting. Select the Background_Music GameObject in the Hierarchy and then disable the checkbox for Play On Awake (Figure 26).

Figure 26: Disabling Play On Awake

Note that when entering Play Mode to preview your Background Music audio, the very beginning may clip. If so, drag the track to the right so that it starts at Frame 5 (Figure 27).

Figure 27: Advancing the Background Music track ahead five frames

5. Create an Audio Track in the Timeline for the cat by selecting + in the SFX Group to add a New Audio Track. With the Audio Track highlighted, right-click and select Add From Audio Clip, then select the audio file titled KM_Cat1_SitPurr.

6. Create another Audio Track in the SFX Group for the dog. Select + in the SFX Group to add a New Audio Track. With the Audio Track highlighted, right-click and then select Add From Audio Clip. Select the audio file titled KM_Dog1_BarkGrowl1 (Figure 28).

Figure 28: The Audio Clips added to the dog and cat tracks in the Timeline’s SFX Group

7. Now that the audio clips are added to the Timeline, let’s arrange each clip’s position by moving them into their proper places. Set the Timeline’s Frame Playhead Cursor to Frame 163. Move and drag the cat’s audio clip to start at Frame 163, and the clip will snap into place (Figure 29).

Figure 29: The cat’s audio clip arranged to start playing at Frame 163.

8. Position the Timeline’s Frame Playhead Cursor to Frame 237. Move the dog’s audio clip to snap it into place at Frame 237 (Figure 30).

Figure 30: The dog’s audio clip to start playing at Frame 237.

9. Add another cat sound effect by right-clicking on the cat’s Timeline track and selecting Add From Audio Clip. Then select the audio file titled KM_Cat_2_HearsDog. Drag the clip to begin playing at Frame 263 (Figure 31).

Figure 31: The cat’s second audio clip arranged to start playing at Frame 263.

10. Add another dog sound effect by right-clicking on the dogs’s track in the Timeline and selecting Add From Audio Clip. Then select the audio file titled KM_Dog_2_BarkLeap. Drag the clip to begin playing at Frame 293 (Figure 32).

Figure 32: The dog’s audio clip arranged to start playing at Frame 293.

11. Add another dog sound effect by right-clicking on the dogs’s track in the Timeline and selecting Add From Audio Clip. Then select the audio file titled KM_Dog_3_RunStart. Drag the clip to begin playing at Frame 336.

12. Repeating the previous steps, add the remaining cat sound effects: KM_Cat_3_Chased1, KM_Cat_4_Chased2, and KM_Cat_5_Unhappy to the Timeline. Place their clips to begin playing at Frame 349, Frame 403, and Frame 490.

13. Add the remaining dog sound effects: KM_Dog_4_RoundsCorner1, KM_Dog_4_RoundsCorner2, KM_Dog_5_Passby, and KM_Dog_6_Bark. Place their clips to begin playing at Frames 374, 397, 419, and 477 (Figure 33).

Figure 33: The individual audio clips arranged at designated intervals along the Timeline

14. Select the Graphs button in the Timeline to expand any audio track’s Spatial Blend, Stereo Pan, and Volume properties for further editing (Figure 34).

Figure 34: The expanded Graph View of the Timeline’s audio tracks

15. In order to make the background music fade in and out, you can edit a sound’s volume level along the Timeline using the Graph editor. To add a keyframe, select the Volume Graph property and then double-click at a designated interval inside the graph. Place two keyframes towards the end of the Timeline’s animation where you intend to start and complete the fade out to silence, then drag the final keyframe downward to fade the volume down over time (Figure 35). Optionally, select the curve handles to customize the curve of the slope.

Figure 35: The Graph view’s keyframes at the end of the Timeline, sloped to fade out the volume.

With Unity’s audio tools, you’re able to mix and trigger environmental sounds, music, and sound effects to enhance your Scene.