diff --git a/spa/plugins/audioconvert/channelmix.c b/spa/plugins/audioconvert/channelmix.c
index fdeb4a038..8b3e33393 100644
--- a/spa/plugins/audioconvert/channelmix.c
+++ b/spa/plugins/audioconvert/channelmix.c
@@ -96,7 +96,12 @@ struct port {
 
 	uint64_t info_all;
 	struct spa_port_info info;
-	struct spa_param_info params[8];
+#define IDX_EnumFormat	0
+#define IDX_Meta	1
+#define IDX_IO		2
+#define IDX_Format	3
+#define IDX_Buffers	4
+	struct spa_param_info params[5];
 
 	struct spa_io_buffers *io;
 
@@ -127,7 +132,9 @@ struct impl {
 	uint64_t info_all;
 	struct spa_node_info info;
 	struct props props;
-	struct spa_param_info params[8];
+#define IDX_PropInfo	0
+#define IDX_Props	1
+	struct spa_param_info params[2];
 
 
 	struct port control_port;
@@ -162,10 +169,10 @@ static void emit_info(struct impl *this, bool full)
 	}
 }
 
-static void emit_params_changed(struct impl *this)
+static void emit_props_changed(struct impl *this)
 {
 	this->info.change_mask |= SPA_NODE_CHANGE_MASK_PARAMS;
-	this->params[1].flags ^= SPA_PARAM_INFO_SERIAL;
+	this->params[IDX_Props].flags ^= SPA_PARAM_INFO_SERIAL;
 	emit_info(this, false);
 }
 
@@ -305,7 +312,7 @@ static int setup_convert(struct impl *this,
 	channelmix_set_volume(&this->mix, this->props.volume, this->props.mute,
 			this->props.n_channel_volumes, this->props.channel_volumes);
 
-	emit_params_changed(this);
+	emit_props_changed(this);
 
 	this->is_passthrough = SPA_FLAG_IS_SET(this->mix.flags, CHANNELMIX_FLAG_IDENTITY);
 
@@ -491,7 +498,7 @@ static int impl_node_set_param(void *object, uint32_t id, uint32_t flags,
 	switch (id) {
 	case SPA_PARAM_Props:
 		if (apply_props(this, param) > 0)
-			emit_params_changed(this);
+			emit_props_changed(this);
 		break;
 	default:
 		return -ENOENT;
@@ -838,11 +845,11 @@ static int port_set_format(void *object,
 
 	port->info.change_mask |= SPA_PORT_CHANGE_MASK_PARAMS;
 	if (port->have_format) {
-		port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_READWRITE);
-		port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, SPA_PARAM_INFO_READ);
+		port->params[IDX_Format] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_READWRITE);
+		port->params[IDX_Buffers] = SPA_PARAM_INFO(SPA_PARAM_Buffers, SPA_PARAM_INFO_READ);
 	} else {
-		port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
-		port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+		port->params[IDX_Format] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+		port->params[IDX_Buffers] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
 	}
 	emit_port_info(this, port, false);
 
@@ -1293,8 +1300,8 @@ impl_init(const struct spa_handle_factory *factory,
 	this->info.flags = SPA_NODE_FLAG_RT;
 	this->info.max_input_ports = 2;
 	this->info.max_output_ports = 1;
-	this->params[0] = SPA_PARAM_INFO(SPA_PARAM_PropInfo, SPA_PARAM_INFO_READ);
-	this->params[1] = SPA_PARAM_INFO(SPA_PARAM_Props, SPA_PARAM_INFO_READWRITE);
+	this->params[IDX_PropInfo] = SPA_PARAM_INFO(SPA_PARAM_PropInfo, SPA_PARAM_INFO_READ);
+	this->params[IDX_Props] = SPA_PARAM_INFO(SPA_PARAM_Props, SPA_PARAM_INFO_READWRITE);
 	this->info.params = this->params;
 	this->info.n_params = 2;
 
@@ -1305,11 +1312,11 @@ impl_init(const struct spa_handle_factory *factory,
 			SPA_PORT_CHANGE_MASK_PARAMS;
 	port->info = SPA_PORT_INFO_INIT();
 	port->info.flags = SPA_PORT_FLAG_DYNAMIC_DATA;
-	port->params[0] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
-	port->params[1] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
-	port->params[2] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
-	port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
-	port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	port->params[IDX_EnumFormat] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
+	port->params[IDX_Meta] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
+	port->params[IDX_IO] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
+	port->params[IDX_Format] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+	port->params[IDX_Buffers] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
 	port->info.params = port->params;
 	port->info.n_params = 5;
 	spa_list_init(&port->queue);
@@ -1322,11 +1329,11 @@ impl_init(const struct spa_handle_factory *factory,
 	port->info = SPA_PORT_INFO_INIT();
 	port->info.flags = SPA_PORT_FLAG_NO_REF |
 		SPA_PORT_FLAG_DYNAMIC_DATA;
-	port->params[0] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
-	port->params[1] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
-	port->params[2] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
-	port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
-	port->params[4] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	port->params[IDX_EnumFormat] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
+	port->params[IDX_Meta] = SPA_PARAM_INFO(SPA_PARAM_Meta, SPA_PARAM_INFO_READ);
+	port->params[IDX_IO] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
+	port->params[IDX_Format] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+	port->params[IDX_Buffers] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
 	port->info.params = port->params;
 	port->info.n_params = 0;
 	spa_list_init(&port->queue);
@@ -1340,10 +1347,11 @@ impl_init(const struct spa_handle_factory *factory,
 	port->info = SPA_PORT_INFO_INIT();
 	port->info.flags = SPA_PORT_FLAG_NO_REF |
 		SPA_PORT_FLAG_DYNAMIC_DATA;
-	port->params[0] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
-	port->params[1] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
-	port->params[2] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
-	port->params[3] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
+	port->params[IDX_EnumFormat] = SPA_PARAM_INFO(SPA_PARAM_EnumFormat, SPA_PARAM_INFO_READ);
+	port->params[IDX_Meta] = SPA_PARAM_INFO(SPA_PARAM_Meta, 0);
+	port->params[IDX_IO] = SPA_PARAM_INFO(SPA_PARAM_IO, SPA_PARAM_INFO_READ);
+	port->params[IDX_Format] = SPA_PARAM_INFO(SPA_PARAM_Format, SPA_PARAM_INFO_WRITE);
+	port->params[IDX_Buffers] = SPA_PARAM_INFO(SPA_PARAM_Buffers, 0);
 	port->info.params = port->params;
 	port->info.n_params = 4;
 	spa_list_init(&port->queue);