Add Configurable DSP with Parametric Equalizer

[maximmaxim345]

Overview

This Pull Request introduces a sophisticated multi-stage Digital Signal Processing (DSP) system to Music Assistant, featuring a highly-flexible Parametric Equalizer as its core component.

Screenshot

For me, the main feature missing from Music Assistant was the lack of a Parametric Equalizer, therefore I added one.

Related Changes

This PR is to be viewed in conjunction with music-assistant/frontend#756 and music-assistant/models#18.

This PR depends on music-assistant/models#18.

Future Filters

This modular system allows the addition of other filters in the future, that I will add in future PRs including:

• Crossfeed: Creates a more natural stereo image by mixing left and right channels
• Basic Tone Controls: replacing CONF_EQ_BASS, CONF_EQ_MID and CONF_EQ_TREBLE
• Compressor: Useful for listening in loud environments
• Limiter: Prevents audio clipping by limiting peak levels
• Convolution: Applies Room Correction filters using impulse responses
• AutoEq: Predefined Equalizers for a large number of Headphones

Implementation Details

DSP Configuration is saved in a separate key compared to all other player configuration.
This has the following advantages:

• Applying changes can be sped up, since main player configuration
  stays the same
• Changing DSP does not require resending Player options as dictated by
  the provider
• Later filters like convolution require special handling for the IR WAV
  file
• This allows saving/loading presets without changing the player's
  configuration

DSP should function with all player providers as I understand, since get_raw_player_config_value is used regardless of the underlying provider.

Tested with DLNA, Chromecast and Sonos.

[marcelveldt]

Wow, just wow. I was kind of hoping someone would pick up the glove for this (as I did prepare a few hooks for this in the code). You just did. Amazing!

I will give this a proper review tomorrow. First impression: Super nice work!

[maximmaxim345]

I'm thinking, maybe this PR (or another PR in the same release) should also add a Tone Controls Filter?

Then we can easily migrate the CONF_EQ_BASS, CONF_EQ_MID and CONF_EQ_TREBLE settings by:

• Automatically adding a "Tone Controls" filter to the default DSP config in case the user previously set CONF_EQ_BASS, CONF_EQ_MID or CONF_EQ_TREBLE
• hiding CONF_EQ_BASS, CONF_EQ_MID and CONF_EQ_TREBLE from the player config UI
• resetting CONF_EQ_BASS, CONF_EQ_MID and CONF_EQ_TREBLE to 0 if a DSP config is saved

Otherwise it would be more difficult to handle this case:

1. The user already uses CONF_EQ_BASS, CONF_EQ_MID or CONF_EQ_TREBLE
2. The user changed the DSP config (by adding a Parametric EQ)
3. The user updated Music Assistant with the "Tone Controls" moved to DSP Config

Let me know, if I should put this in this set of PRs or open another one.