Exoplayer Pitch Xamarin forms

I used exoplayer into my xamarin forms cross platform app.
Regarding the pitch, I want range between -4 to + 4 semitones.
I used code for set pitch

var _context = global::Android.App.Application.Context;
 var defaultBandwidthMeter = new DefaultBandwidthMeter();
 var adaptiveTrackSelectionFactory = new AdaptiveTrackSelection.Factory(defaultBandwidthMeter);
 var defaultTrackSelector = new DefaultTrackSelector(adaptiveTrackSelectionFactory);
SimpleExoPlayer _player = ExoPlayerFactory.NewSimpleInstance(_context, defaultTrackSelector);
PlaybackParameters parameters = new PlaybackParameters(speed, pitch);
player.PlaybackParameters=parameters;

speed, pitch are the two variable.
How to apply pitch value (-4). I know negative pitch is not supported on Exoplayer.
But my requirement is , I can change pitch frequently -4 to +4. How it posssible. Please know me a possible way. I am waiting for response.