For USB devices the latency jitter strongly depends on device latency. Therefore
a boolean low_device_latency parameter is introduced to half the device latency.
Normally 1/3 of the configured end-to-end latency is used, with the parameter
this is changed to 1/6. In many situations the parameter can improve latency
stability but it will also lead to significantly higher CPU consumption.
---
src/modules/module-loopback.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/src/modules/module-loopback.c b/src/modules/module-loopback.c
index eeb93264..048fe4f9 100644
--- a/src/modules/module-loopback.c
+++ b/src/modules/module-loopback.c
@@ -46,6 +46,7 @@ PA_MODULE_USAGE(
"adjust_time=<how often to readjust rates in s> "
"latency_msec=<latency in ms> "
"max_latency_msec=<maximum latency in ms> "
+ "low_device_latency=<boolean, use half of the normal device latency> "
"adjust_threshold_usec=<threshold for latency adjustment in usec> "
"format=<sample format> "
"rate=<sample rate> "
@@ -98,6 +99,7 @@ struct userdata {
pa_usec_t max_latency;
pa_usec_t adjust_time;
uint32_t adjust_threshold;
+ bool low_device_latency;
/* Latency boundaries and current values */
pa_usec_t min_source_latency;
@@ -189,6 +191,7 @@ static const char* const valid_modargs[] = {
"adjust_time",
"latency_msec",
"max_latency_msec",
+ "low_device_latency",
"adjust_threshold_usec",
"format",
"rate",
@@ -776,11 +779,14 @@ static void update_effective_source_latency(struct userdata *u, pa_source *sourc
* Set source output latency to one third of the overall latency if possible.
* The choice of one third is rather arbitrary somewhere between the minimum
* possible latency which would cause a lot of CPU load and half the configured
- * latency which would quickly lead to underruns */
+ * latency which would quickly lead to underruns. In low device latency mode set
+ * source to one sixth of the overall latency. */
static void set_source_output_latency(struct userdata *u, pa_source *source) {
pa_usec_t latency, requested_latency;
requested_latency = u->latency / 3;
+ if (u->low_device_latency)
+ requested_latency = u->latency / 6;
/* Normally we try to configure sink and source latency equally. If the
* sink latency cannot match the requested source latency try to set the
@@ -1149,11 +1155,14 @@ static int sink_input_process_msg_cb(pa_msgobject *obj, int code, void *data, in
* Set sink input latency to one third of the overall latency if possible.
* The choice of one third is rather arbitrary somewhere between the minimum
* possible latency which would cause a lot of CPU load and half the configured
- * latency which would quickly lead to underruns. */
+ * latency which would quickly lead to underruns. In low device latency mode
+ * set sink to one sixth of the overall latency. */
static void set_sink_input_latency(struct userdata *u, pa_sink *sink) {
pa_usec_t latency, requested_latency;
requested_latency = u->latency / 3;
+ if (u->low_device_latency)
+ requested_latency = u->latency / 6;
/* Normally we try to configure sink and source latency equally. If the
* source latency cannot match the requested sink latency try to set the
@@ -1482,6 +1491,7 @@ int pa__init(pa_module *m) {
uint32_t adjust_time_sec;
const char *n;
bool remix = true;
+ bool low_device_latency = false;
pa_assert(m);
@@ -1574,6 +1584,11 @@ int pa__init(pa_module *m) {
max_latency_msec = latency_msec;
}
+ if (pa_modargs_get_value_boolean(ma, "low_device_latency", &low_device_latency) < 0) {
+ pa_log("Invalid boolean device latency parameter");
+ goto fail;
+ }
+
m->userdata = u = pa_xnew0(struct userdata, 1);
u->core = m->core;
u->module = m;
@@ -1594,6 +1609,7 @@ int pa__init(pa_module *m) {
u->latency_error = 0;
u->adjust_threshold = adjust_threshold;
u->target_latency_cross_counter = 0;
+ u->low_device_latency = low_device_latency;
u->initial_adjust_pending = true;
adjust_time_sec = DEFAULT_ADJUST_TIME_USEC / PA_USEC_PER_SEC;
--
2.14.1
