How to improve the metrics of a hyper-casual game by enhancing its sound?

The column was authored by Vladimir Korobeynikov, the founder of the studio, and Maria Zhulanova, sound designer and composer for koro.games.

Vladimir Korobeynikov and Maria Zhulanova

Since the early 2000s, sound in video games has become a hot topic among developers and players alike. Sound design has started being perceived not just as an addition but as an integral part of the gaming experience.

One of the pioneers in showing the importance of music and sound for creating a game's atmosphere was Trent Reznor. His work on the soundtrack for Quake set new standards for the industry.

Since then, the gaming industry has made tremendous progress. Audio technologies have evolved alongside it. Nowadays, games on consoles and PCs support adaptive music, three-dimensional soundscapes, and immersive audio.

Moreover, sound design has become a tool that can significantly impact players' perceptions, aid in storytelling, and affect player retention and engagement. Consider, for example, what experts at King say about sound.

Indeed, this article is dedicated to exploring how audio can enhance metrics by testing this hypothesis.

Research Through A/B Testing

To see how audio content affects key in-game metrics and player behavior, we used our own project in a popular genre with a steady influx of new players — War of Rafts.

Currently, the game has over 100 million downloads across various platforms, and its monthly active users (MAU) number reaches 2 million. Every month, 800,000 new users install the game.

After selecting the game, we analyzed its audio solutions.

Based on this analysis, new sounds were created, and music was composed (noteworthy: music was initially absent from the game), which then fulfilled important roles such as:

• Conveying information about on-screen happenings to players;
• Encouraging and reinforcing player actions;
• Creating a pleasant game flow.

We began verifying the impact of the new audio on game metrics through A/B testing.

On the main game page, a new build was published, accessible to 20% of users. Only the audio differed in this build.

This approach is a good solution as it ensures the purity of measurements by eliminating the effects of other innovations.

The A/B testing was conducted in two stages.

• During the first stage, we compared the behavior of two user groups. The control group played the original game version. The second experienced the game with new sound effects.
• In the second stage of testing, we had three user groups: (1) a control group, (2) playing with the new sound, and (3) playing with new sound and music.

This setup allowed us to quantify the impact of all aspects of the audio experience on metrics.

Data collection for each test lasted about two weeks.

In the first test, 135,000 players participated:

• 108,000 played with the previous sound version;
• 27,000 with the updated version.

In the second test, 153,000 players participated:

• 125,000 played with the old sound version;
• 27,000 with the new version.

Case Study

We won't delve into all the tests. Instead, we'll focus on how the music was composed and examine the sound design for one key game mechanic in detail.

Music

When working on music, it's crucial to remember that it's a powerful tool influencing emotions, and thus player engagement. It's essential to apply it correctly.

One of the best books on this topic was written by Are Brean and Geir Olve Skeie titled “Music and the Brain”. The book presents scientific facts and studies about what happens in the brain when it hears sounds and music.

Now, back to the game.

In War of Rafts, the player moves on a floating platform. Along the way, the player docks with other platforms usually occupied by enemies. After defeating them, the enemy's platform merges with the player's platform.

This is how the game looks from the outside, but we internally divide the gameplay into two parts:

• Exploring the territory (collecting items, trial skirmishes);
• Boss battles.

Based on this, we decided on our track composition approach.

The first part of the track, played during exploration, is light and calm. It aims to support the player and immerse them into the game world. The second track part, starting during boss battles, is more rhythmic, with a heroic tone. It plays throughout the fight and provides emotional backing to the player.

Case Study with Rewarded Ads

The game also features platforms with weapons/skins. These items are valuable to players as they increase their power and enhance their chances against strong opponents. To acquire them, players must dock with the platform and view an advertisement.

In our research, we considered how to further increase dockings to such platforms (i.e., how to motivate players to do so more often). We hypothesized that the sound of docking should highlight the advantage of receiving a bonus (this sound was initially absent).

To achieve this effect, we decided to add a complex sound design:

• A voice layer saying "Mega gun" or "Free skin" (recorded using a male voice with a rich, dense timbre, both warlike and supportive);
• A tonal component;
• A layer of mechanical sounds suggesting that weapons or skins are ready for use.

Examples of new sounds

After conducting A/B tests, we noticed that players were interacting with these platforms more frequently. Simultaneously, the number of rewarded ad views increased:

• In the game version with new sound, ad views increased by 2.50%;
• In a version with both new sound and music, ad views increased by 3.38%.

Other Results

As noted earlier, we decided not to delve into all the hypotheses tested and changes made during our study in this article.

Instead, we found it important to highlight how the new sound generally impacted the metrics.

• Ad LTV increased by 4%. The positive effect was particularly notable on the LTV of long-time players.
• The revival via ad viewing decreased by 0.5% to 2.95% in the version with only new sound, but increased to 3.7% after adding music.
• Adding music boosted engagement with the game's economy, increasing in-game currency purchases.
• The win-to-loss ratio rose from 57% to 62%.
• Average daily gameplay time grew from 31 minutes to 37.3 minutes, a 20.3% increase, after the new sounds were added.
• With the addition of music, the percentage of players playing consecutively days significantly increased. The first-day retention with the new sound increased by 0.9 percentage points, while with both new sound and music, it grew by 9.5 percentage points.

Sound improvements positively impact Timespent (minutes)

Interestingly, before our study, we attempted to determine the percentage of players who play with sound. However, we couldn’t determine this because the user agreement prevents us from tracking whether device sound is on.

While the lack of this information might seem critical, questioning the validity of efforts in this area, the results above show it is not as crucial. Ultimately, it’s important that we can track the overall effect of these changes.

These conclusions mark the beginning of our efforts to rethink sound design approaches. In the future, we also plan to study the impact of dynamic soundtracks on audience behavior.