Could there be an Equalizer?

[TreeTrunk221]

Could you add an equalizer? For reference, the app Musi has one that is pretty good.

[othyn]

Same. I just went hunting for one on iOS and it appears there currently isn't a way to do this?

My headphones sound a little bright and I would like to tweak a few things.

[Chaphasilor]

Like with so many things the answer is: only on Android

We use a plugin called just_audio for audio playback, which handles most of the different platforms (Android, iOS, etc.) for us, in a relatively consistent way. This vastly simplifies things for us, otherwise such a cross-platform audio player would be even more work.

Sadly, just_audio only supports equalizers on Android, not iOS or other platforms. I actually think there's no way to configure an equalizer into the media player on iOS at all, aside from building everything yourself. This only works for apps that directly deal with audio samples, like Logic Pro, because they have a different audio pipeline than simple media players.

On Android there's also a system-wide equalizer that can be used instead, so there's less need for the feature. And adding this feature just for Android currently isn't worth the effort in my opinion.

That being said, if anyone wants to give this a try, I'd be happy to accept a PR!
The code would be very similar to what is being used for the volume normalization, so the following section should contain almost all needed "concepts". Building the UI for configuring the equalizer will be the most challenging part though.

finamp/lib/services/music_player_background_task.dart

Lines 53 to 121 in 5a33802

	_androidAudioEffects = [];
	_iosAudioEffects = [];
	if (Platform.isAndroid) {
	_loudnessEnhancerEffect = AndroidLoudnessEnhancer();
	_androidAudioEffects.add(_loudnessEnhancerEffect!);
	} else {
	_loudnessEnhancerEffect = null;
	}
	_audioPipeline = AudioPipeline(
	androidAudioEffects: _androidAudioEffects,
	darwinAudioEffects: _iosAudioEffects,
	);
	_player = AudioPlayer(
	audioLoadConfiguration: AudioLoadConfiguration(
	androidLoadControl: AndroidLoadControl(
	minBufferDuration: FinampSettingsHelper.finampSettings.bufferDuration,
	maxBufferDuration: FinampSettingsHelper
	.finampSettings.bufferDuration *
	1.5, // allows the player to fetch a bit more data in exchange for reduced request frequency
	prioritizeTimeOverSizeThresholds: true,
	),
	darwinLoadControl: DarwinLoadControl(
	preferredForwardBufferDuration:
	FinampSettingsHelper.finampSettings.bufferDuration,
	),
	),
	audioPipeline: _audioPipeline,
	);
	_loudnessEnhancerEffect?.setEnabled(
	FinampSettingsHelper.finampSettings.volumeNormalizationActive);
	_loudnessEnhancerEffect?.setTargetGain(0.0 /
	10.0); //!!! always divide by 10, the just_audio implementation has a bug so it expects a value in Bel and not Decibel (remove once https://github.com/ryanheise/just_audio/pull/1092/commits/436b3274d0233818a061ecc1c0856a630329c4e6 is merged)
	// calculate base volume gain for iOS as a linear factor, because just_audio doesn't yet support AudioEffect on iOS
	iosBaseVolumeGainFactor = pow(
	10.0,
	FinampSettingsHelper.finampSettings.volumeNormalizationIOSBaseGain /
	20.0)
	as double; // https://sound.stackexchange.com/questions/38722/convert-db-value-to-linear-scale
	if (!Platform.isAndroid) {
	_volumeNormalizationLogger.info(
	"non-Android base volume gain factor: $iosBaseVolumeGainFactor");
	}
	// Propagate all events from the audio player to AudioService clients.
	_player.playbackEventStream.listen((event) async {
	playbackState.add(_transformEvent(event));
	});
	FinampSettingsHelper.finampSettingsListener.addListener(() {
	// update replay gain settings every time settings are changed
	iosBaseVolumeGainFactor = pow(
	10.0,
	FinampSettingsHelper
	.finampSettings.volumeNormalizationIOSBaseGain /
	20.0)
	as double; // https://sound.stackexchange.com/questions/38722/convert-db-value-to-linear-scale
	if (FinampSettingsHelper.finampSettings.volumeNormalizationActive) {
	_loudnessEnhancerEffect?.setEnabled(true);
	_applyVolumeNormalization(mediaItem.valueOrNull);
	} else {
	_loudnessEnhancerEffect?.setEnabled(false);
	_player.setVolume(1.0); // disable replay gain on iOS
	_volumeNormalizationLogger.info("Replay gain disabled");
	}
	});

[jmshrv]

Having a poke about with the iOS version of Plexamp, both AudioToolbox and AVKit, whereas just_audio uses AVFoundation.

AudioToolbox is a much more low-level API, so it's likely that Plexamp is doing some very custom audio handling, while just_audio is just using the built in player from iOS/macOS.

With a bit more digging (searching the program text for OPUS to see if libopus was anywhere lol), I found references to BASS, so it's likely that Plexamp is using this library to feed into iOS via AudioToolbox. I'm no reverse engineer so I can't really verify it (also Plexamp is a React Native app so the code is a bit all over the place), but this is probably enough speculation for now :)

Fun fact: one of the reasons I started making Finamp was because Plexamp's Android app couldn't handle surround FLACs (it'd just drop channels that weren't L and R), so the few SACDs I had in my collection were unlistenable 🙃

[jmshrv]

Forgot to say - with this, Plexamp has full control over audio samples, so can do EQ on its own

[jmshrv]

and yep, looks like BASS handles EQ on its own

[jmshrv]

(^ @othyn, just in case you're not watching this thread)

[othyn]

That's a super interesting deep dive, thank you for sharing! I really should brush up on some reverse engineering, as it's really awesome to see what you've been able to find.