Move audio adjustment hookup to own method for clarity

osu.Game/Rulesets/Mods/ModAdaptiveSpeed.cs

@@ -126,7 +126,8 @@ namespace osu.Game.Rulesets.Mods
 
         public ModAdaptiveSpeed()
         {
-            rateAdjustHelper = new RateAdjustModHelper(SpeedChange, AdjustPitch);
+            rateAdjustHelper = new RateAdjustModHelper(SpeedChange);
+            rateAdjustHelper.HandleAudioAdjustments(AdjustPitch);
 
             InitialRate.BindValueChanged(val =>
             {

osu.Game/Rulesets/Mods/ModDoubleTime.cs

@@ -34,7 +34,8 @@ namespace osu.Game.Rulesets.Mods
 
         protected ModDoubleTime()
         {
-            rateAdjustHelper = new RateAdjustModHelper(SpeedChange, AdjustPitch);
+            rateAdjustHelper = new RateAdjustModHelper(SpeedChange);
+            rateAdjustHelper.HandleAudioAdjustments(AdjustPitch);
         }
 
         public override void ApplyToTrack(IAdjustableAudioComponent track)

osu.Game/Rulesets/Mods/ModHalfTime.cs

@@ -34,7 +34,8 @@ namespace osu.Game.Rulesets.Mods
 
         protected ModHalfTime()
         {
-            rateAdjustHelper = new RateAdjustModHelper(SpeedChange, AdjustPitch);
+            rateAdjustHelper = new RateAdjustModHelper(SpeedChange);
+            rateAdjustHelper.HandleAudioAdjustments(AdjustPitch);
         }
 
         public override void ApplyToTrack(IAdjustableAudioComponent track)

osu.Game/Rulesets/Mods/ModTimeRamp.cs

@@ -48,7 +48,8 @@ namespace osu.Game.Rulesets.Mods
 
         protected ModTimeRamp()
         {
-            rateAdjustHelper = new RateAdjustModHelper(SpeedChange, AdjustPitch);
+            rateAdjustHelper = new RateAdjustModHelper(SpeedChange);
+            rateAdjustHelper.HandleAudioAdjustments(AdjustPitch);
 
             // for preview purpose at song select. eventually we'll want to be able to update every frame.
             FinalRate.BindValueChanged(_ => applyRateAdjustment(double.PositiveInfinity), true);

osu.Game/Rulesets/Mods/RateAdjustModHelper.cs

@@ -1,6 +1,7 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
 using osu.Framework.Audio;
 using osu.Framework.Bindables;
 
@@ -11,17 +12,32 @@ namespace osu.Game.Rulesets.Mods
     /// </summary>
     public class RateAdjustModHelper : IApplicableToTrack
     {
-        private readonly BindableBool? adjustPitch;
         private readonly BindableNumber<double> speedChange;
+
         private IAdjustableAudioComponent? track;
 
-        public RateAdjustModHelper(BindableNumber<double> speedChange, BindableBool? adjustPitch = null)
+        private BindableBool? adjustPitch;
+
+        /// <summary>
+        /// Construct a new <see cref="RateAdjustModHelper"/>.
+        /// </summary>
+        /// <param name="speedChange">The main speed adjust parameter which is exposed to the user.</param>
+        public RateAdjustModHelper(BindableNumber<double> speedChange)
         {
             this.speedChange = speedChange;
+        }
+
+        /// <summary>
+        /// Setup audio track adjustments for a rate adjust mod.
+        /// Importantly, <see cref="ApplyToTrack"/> must be called when a track is obtained/changed for this to work.
+        /// </summary>
+        /// <param name="adjustPitch">The "adjust pitch" setting as exposed to the user.</param>
+        public void HandleAudioAdjustments(BindableBool adjustPitch)
+        {
             this.adjustPitch = adjustPitch;
 
             // When switching between pitch adjust, we need to update adjustments to time-shift or frequency-scale.
-            adjustPitch?.BindValueChanged(adjustPitchSetting =>
+            adjustPitch.BindValueChanged(adjustPitchSetting =>
             {
                 track?.RemoveAdjustment(adjustmentForPitchSetting(adjustPitchSetting.OldValue), speedChange);
                 track?.AddAdjustment(adjustmentForPitchSetting(adjustPitchSetting.NewValue), speedChange);
@@ -31,12 +47,23 @@ namespace osu.Game.Rulesets.Mods
             });
         }
 
+        /// <summary>
+        /// Should be invoked when a track is obtained / changed.
+        /// </summary>
+        /// <param name="track">The new track.</param>
+        /// <exception cref="InvalidOperationException">If this method is called before <see cref="HandleAudioAdjustments"/>.</exception>
         public void ApplyToTrack(IAdjustableAudioComponent track)
         {
+            if (adjustPitch == null)
+                throw new InvalidOperationException($"Must call {nameof(HandleAudioAdjustments)} first");
+
             this.track = track;
-            adjustPitch?.TriggerChange();
+            adjustPitch.TriggerChange();
         }
 
+        /// <summary>
+        /// The score multiplier for the current <see cref="speedChange"/>.
+        /// </summary>
         public double ScoreMultiplier
         {
             get