Simplify audio muting.

Zero out the audio buffer instead of muting the codec. The HPF (and other downstream signal processing) can continue running, not produce discontinuities from being effectively halted during mute.

firmware/baseband/main.cpp

@@ -429,17 +429,6 @@ class BasebandProcessor {
 		feed_audio_stats(audio);
 	}
 
-	void mute_audio_buffer() {
-		auto audio_buffer = audio::dma::tx_empty_buffer();;
-		for(size_t i=0; i<audio_buffer.count; i++) {
-			audio_buffer.p[i].left = audio_buffer.p[i].right = 0;
-		}
-		i2s::i2s0::tx_unmute();
-
-		// TODO: No hard-coded audio sampling rate!
-		mute_audio_stats(audio_buffer.count, 48000);
-	}
-
 private:
 	BlockDecimator<256> channel_spectrum_decimator { 4 };
 
@@ -474,16 +463,6 @@ class BasebandProcessor {
 		);
 	}
 
-	void mute_audio_stats(const size_t count, const size_t sampling_rate) {
-		audio_stats.mute(
-			count,
-			sampling_rate,
-			[this](const AudioStatistics statistics) {
-				this->post_audio_stats_message(statistics);
-			}
-		);
-	}
-
 	void post_audio_stats_message(const AudioStatistics statistics) {
 		if( audio_stats_message.is_free() ) {
 			audio_stats_message.statistics = statistics;
@@ -572,15 +551,19 @@ class NarrowbandFMAudio : public BasebandProcessor {
 		auto audio = demod.execute(channel, work_audio_buffer);
 
 		static uint64_t audio_present_history = 0;
-		const auto audio_present = squelch.execute(audio);
-		audio_present_history = (audio_present_history << 1) | (audio_present ? 1 : 0);
-
-		if( audio_present_history ) {
-			audio_hpf.execute_in_place(audio);
-			fill_audio_buffer(audio);
-		} else {
-			mute_audio_buffer();
+		const auto audio_present_now = squelch.execute(audio);
+		audio_present_history = (audio_present_history << 1) | (audio_present_now ? 1 : 0);
+		const bool audio_present = (audio_present_history != 0);
+
+		if( !audio_present ) {
+			// Zero audio buffer.
+			for(size_t i=0; i<audio.count; i++) {
+				audio.p[i] = 0;
+			}
 		}
+
+		audio_hpf.execute_in_place(audio);
+		fill_audio_buffer(audio);
 	}
 
 private:
@@ -727,7 +710,7 @@ class FSKProcessor : public BasebandProcessor {
 
 		auto demodulated = demod.execute(channel, work_demod_buffer);
 
-		mute_audio_buffer();
+		i2s::i2s0::tx_mute();
 
 		for(size_t i=0; i<demodulated.count; i++) {
 			clock_recovery.execute(demodulated.p[i], symbol_handler_fn);