How to play a sound with variations
One of the ways to make your machine more professional is to use different variations of sounds in your machine. This will add variety and make your audio less predictable and more "alive". This guide explains how to play a sound with multiple variations in your machine. Sound support is part of the MPF media controller and only available if you're using MPF-MC for your media controller. This guide assumes you have already configured your sound system for your machine and are familiar with the basic sound setup concepts. If not, please start with the Setting up sound for your machine guide first.
1. An brief introduction to sound pools
Sound pools allow you to group multiple sounds together and treat the pool as a single sound. Each time a sound pool is played, it selects a sound from its group of sounds. The selection can be configured to be random or in a particular sequence. For more complete information, please read the sound_pools documentation.
Although sound pools can be used to play a random music track or random callout when an event occurs, in this guide we will be using a sound pool to play variations of a sound when a slingshot is hit.
2. Add a sound and some variations
Before we can create our sound pool, we first need to configure the
individual sounds that will make up our pool. We've decided we want to
have a small ding (like a triangle hit) play whenever the slingshot is
hit. Let's start by adding our basic sound to our sound assets. The
hardest part of this process is to either generate or find the sound you
want (we won't go into that process here). Once you have your sound
file, put it in the appropriate sound asset folder. I found a simple
triangle sound on www.freesound.org that
we'll use here, 13147__looppool__triangle1.wav. Place the file in
your sound effects track folder (
we'll add it to your machine configuration file, but give it an easier
name to remember (
triangle_01) using the
file: setting (or you could
simply rename the file to triangle_01.wav and omit the file:
Now add a few variations of the sound. I used my favorite sound editor
to slightly adjust the pitch and frequency content of the triangle sound
file, creating three variations. You can also just find some other
similar sounds on the internet. After you have your variations, place
them in the same directory as your first sound file. We are now ready to
add them to the
sounds: section in the machine configuration file (I
named the sound variations triangle_02, triangle_03, and
3. Configure the sound pool
We now have 4 variations of the same basic triangle sound. It's time to
put them all into a single sound pool object so we can treat them as a
single sound. To do so, we need to add a
sound_pools: section to our
machine configuration file as follows:
We now have a sound pool asset called
triangle that acts just like a
sound asset, except that each time
triangle is played, one of the 4
sound variations contained in the sound pool will randomly be selected
to be played. Want to add more variations or take one out? It's just as
simple as modifying the list of sounds in the sound pool.
This is great, but let's adjust the sound pool settings a bit to fine
tune its behavior. We really want the main sound (
triangle_01) to be
played more often than the other sounds. How can we make that happen?
It's very easy to do. We can add weights to each sound in the pool that
specify the probability of each sound being selected. Let's look at our
sound_pools: section again:
Notice we've added a pipe character (
|) to the end of each sound
followed by a numeric value. These values assign a relative weight to
each sound that will be used in the random selection process.
triangle_01 has a relative weight of
5 out of a total weighting of
10 (simply add all the weight values), therefore its probability of
being selected is
|1 appended to
unnecessary because a relative weight of
1 is the default value for
all sounds in the pool that do not have explicit weight values assigned.
Sometimes you may want to have sounds included based on conditional events. You can add a condition to any sound and the sound pool will only include that sound if the condition evaluates to true at playback time. If the selection is random, excluded events will not be weighted in the distribution. If the selection is sequential, excluded events will simply be skipped.
Sound conditions are formatted the same as all conditional events. Any sound in a pool can have a weight, a condition, both, or neither.
For additional sound pool setting options, take a look at the sound_pools documentation.
4. Configuring the sound player
We have our sounds and sound pool configured. To trigger the sounds with MPF events, the sound player can be used. The sound player was covered in the previous tutorial and will not be covered again here. You can also read the sound_player documentation.
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