effect: Add NO_DITHER flag.

Author: bmc0

dsp.c

@@ -1,7 +1,7 @@
 /*
  * This file is part of dsp.
  *
- * Copyright (c) 2013-2024 Michael Barbour <[email protected]>
+ * Copyright (c) 2013-2025 Michael Barbour <[email protected]>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -38,9 +38,9 @@
 	(((x) == 0) ? (in_codecs.head == NULL || input_mode == INPUT_MODE_SEQUENCE) ? DEFAULT_FS : in_codecs.head->fs : (x))
 #define CHOOSE_INPUT_CHANNELS(x) \
 	(((x) == 0) ? (in_codecs.head == NULL || input_mode == INPUT_MODE_SEQUENCE) ? DEFAULT_CHANNELS : in_codecs.head->channels : (x))
-#define SHOULD_DITHER(in, out, has_effects) \
+#define SHOULD_DITHER(in, out, chain_dither) \
 	(force_dither != -1 && ((out)->hints & CODEC_HINT_CAN_DITHER) && \
-		(force_dither == 1 || ((out)->prec < 24 && ((has_effects) || (in)->prec > (out)->prec || !((in)->hints & CODEC_HINT_CAN_DITHER)))))
+		(force_dither == 1 || ((out)->prec < 24 && ((chain_dither) || (in)->prec > (out)->prec || !((in)->hints & CODEC_HINT_CAN_DITHER)))))
 #define TIME_FMT "%.2zd:%.2zd:%05.2lf"
 #define TIME_FMT_ARGS(frames, fs) \
 	((frames) != -1) ? (frames) / (fs) / 3600 : 0, \
@@ -625,6 +625,7 @@ static void handle_tstp(int is_paused)
 			if (init_out_codec(&out_p, &stream, -1, write_buf_blocks) == NULL) \
 				cleanup_and_exit(1); \
 		} \
+		chain_dither = effects_chain_needs_dither(&chain); \
 	} while (0)
 
 #define REALLOC_BUFS \
@@ -639,7 +640,8 @@ static void handle_tstp(int is_paused)
 
 int main(int argc, char *argv[])
 {
-	int is_paused = 0, do_dither = 0, chain_start, chain_argc, term_sig, err;
+	int is_paused = 0, do_dither = 0, term_sig, err;
+	int chain_start, chain_argc, chain_dither;
 	int read_buf_blocks = 0;
 	double in_time = 0.0;
 	struct codec *c = NULL;
@@ -753,11 +755,12 @@ int main(int argc, char *argv[])
 		int buf_len = 0;
 		REALLOC_BUFS;
 		dither_mult = tpdf_dither_get_mult(out_codec->prec);
+		chain_dither = effects_chain_needs_dither(&chain);
 
 		while (in_codecs.head != NULL) {
 			ssize_t r, pos = 0;
 			int k = 0;
-			do_dither = SHOULD_DITHER(in_codecs.head, out_codec, chain.head != NULL);
+			do_dither = SHOULD_DITHER(in_codecs.head, out_codec, chain_dither);
 			LOG_FMT(LL_VERBOSE, "info: dither %s", (do_dither) ? "on" : "off" );
 			print_io_info(in_codecs.head, LL_NORMAL, "input");
 			print_progress(in_codecs.head, pos, is_paused, 1);
@@ -826,7 +829,7 @@ int main(int argc, char *argv[])
 							}
 							else REOPEN_OUTPUT;
 							REALLOC_BUFS;
-							do_dither = SHOULD_DITHER(in_codecs.head, out_codec, chain.head != NULL);
+							do_dither = SHOULD_DITHER(in_codecs.head, out_codec, chain_dither);
 							LOG_FMT(LL_VERBOSE, "info: dither %s", (do_dither) ? "on" : "off" );
 							break;
 						case 'v':

effect.c

@@ -401,6 +401,17 @@ ssize_t get_effects_chain_max_out_frames(struct effects_chain *chain, ssize_t in
 	return frames;
 }
 
+int effects_chain_needs_dither(struct effects_chain *chain)
+{
+	struct effect *e = chain->head;
+	while (e != NULL) {
+		if (!(e->flags & EFFECT_FLAG_NO_DITHER))
+			return 1;
+		e = e->next;
+	}
+	return 0;
+}
+
 sample_t * run_effects_chain(struct effect *e, ssize_t *frames, sample_t *buf1, sample_t *buf2)
 {
 	sample_t *ibuf = buf1, *obuf = buf2, *tmp;

effect.h

@@ -32,6 +32,7 @@ struct effect_info {
 enum {
 	EFFECT_FLAG_PLOT_MIX        = 1<<0,
 	EFFECT_FLAG_OPT_REORDERABLE = 1<<1,
+	EFFECT_FLAG_NO_DITHER       = 1<<2,  /* does not modify the signal such that dither is useful */
 };
 
 struct effect {
@@ -72,6 +73,7 @@ void append_effect(struct effects_chain *, struct effect *);
 int build_effects_chain(int, const char *const *, struct effects_chain *, struct stream_info *, const char *);
 ssize_t get_effects_chain_buffer_len(struct effects_chain *, ssize_t, int);
 ssize_t get_effects_chain_max_out_frames(struct effects_chain *, ssize_t);
+int effects_chain_needs_dither(struct effects_chain *);
 sample_t * run_effects_chain(struct effect *, ssize_t *, sample_t *, sample_t *);
 double get_effects_chain_delay(struct effects_chain *);
 void reset_effects_chain(struct effects_chain *);

remix.c

@@ -138,14 +138,15 @@ struct effect * remix_effect_init(const struct effect_info *ei, const struct str
 
 	state = calloc(1, sizeof(struct remix_state));
 	state->channel_selectors = calloc(out_channels, sizeof(char *));
-	int use_run_1a = 1, use_run_4 = 1;
+	int use_run_1a = 1, use_run_4 = 1, set_no_dither = 1;
 	for (int k = 0, i = 0, ch = 0; k < out_channels; ++k, ++ch) {
 		state->channel_selectors[k] = NEW_SELECTOR(istream->channels);
 		if (ch >= istream->channels || GET_BIT(channel_selector, ch)) {
 			if (i < n_selectors) {
 				if (strcmp(argv[i+1], ".") != 0 && parse_selector_masked(argv[i+1], state->channel_selectors[k], channel_selector, istream->channels))
 					goto fail;
 				const int n_sel = num_bits_set(state->channel_selectors[k], istream->channels);
+				if (n_sel > 1) set_no_dither = 0;
 				if (n_sel != 1) use_run_1a = 0;
 				if (n_sel > 4) use_run_4 = 0;
 				++i;
@@ -170,6 +171,7 @@ struct effect * remix_effect_init(const struct effect_info *ei, const struct str
 	e->istream.channels = istream->channels;
 	e->ostream.channels = out_channels;
 	e->flags |= EFFECT_FLAG_PLOT_MIX;
+	if (set_no_dither) e->flags |= EFFECT_FLAG_NO_DITHER;
 	if (use_run_1a) {
 		state->fast_sel.s1 = calloc(out_channels, sizeof(int));
 		for (int k = 0; k < out_channels; ++k) {

stats.c

@@ -1,7 +1,7 @@
 /*
  * This file is part of dsp.
  *
- * Copyright (c) 2014-2024 Michael Barbour <[email protected]>
+ * Copyright (c) 2014-2025 Michael Barbour <[email protected]>
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -127,6 +127,7 @@ struct effect * stats_effect_init(const struct effect_info *ei, const struct str
 	e->name = ei->name;
 	e->istream.fs = e->ostream.fs = istream->fs;
 	e->istream.channels = e->ostream.channels = istream->channels;
+	e->flags |= EFFECT_FLAG_NO_DITHER;
 	e->run = stats_effect_run;
 	e->plot = stats_effect_plot;
 	e->destroy = stats_effect_destroy;