add optional modulators to synth/voices

synth/tx_voice.h

@@ -5,6 +5,7 @@
 #include "tx_operator.h"
 #include "tx_sineosc.h"
 #include "tx_parameter_mapping.h"
+#include <span>
 
 namespace trnr {
 
@@ -48,7 +49,7 @@ public:
 	// modulates the pitch in semitones
 	void modulate_pitch(float _pitch) override { this->pitch_mod = _pitch; }
 
-	void process_samples(t_sample** _outputs, int _start_index, int _block_size) override
+	void process_samples(t_sample** _outputs, int _start_index, int _block_size, std::span<std::span<t_sample>> _modulators = {}) override
 	{
 		float frequency = midi_to_frequency(midi_note + pitch_mod + additional_pitch_mod);