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timefilter.h File Reference

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TimeFilterff_timefilter_new (double clock_period, double feedback2_factor, double feedback3_factor)
 Create a new Delay Locked Loop time filter. More...
double ff_timefilter_update (TimeFilter *self, double system_time, double period)
 Update the filter. More...
double ff_timefilter_eval (TimeFilter *self, double delta)
 Evaluate the filter at a specified time. More...
void ff_timefilter_reset (TimeFilter *)
 Reset the filter. More...
void ff_timefilter_destroy (TimeFilter *)
 Free all resources associated with the filter. More...

Function Documentation

TimeFilter* ff_timefilter_new ( double  clock_period,
double  feedback2_factor,
double  feedback3_factor 

Create a new Delay Locked Loop time filter.

feedback2_factor and feedback3_factor are the factors used for the multiplications that are respectively performed in the second and third feedback paths of the loop.

Unless you know what you are doing, you should set these as follow:

o = 2 * M_PI * bandwidth * period_in_seconds feedback2_factor = sqrt(2) * o feedback3_factor = o * o

Where bandwidth is up to you to choose. Smaller values will filter out more of the jitter, but also take a longer time for the loop to settle. A good starting point is something between 0.3 and 3 Hz.

time_baseperiod of the hardware clock in seconds (for example 1.0/44100)
periodexpected update interval, in input units
brandwidthfiltering bandwidth, in Hz
a pointer to a TimeFilter struct, or NULL on error

For more details about these parameters and background concepts please see: http://www.kokkinizita.net/papers/usingdll.pdf

Definition at line 46 of file timefilter.c.

Referenced by audio_read_header(), init_convert_timestamp(), main(), pulse_read_header(), and start_jack().

double ff_timefilter_update ( TimeFilter self,
double  system_time,
double  period 

Update the filter.

This function must be called in real time, at each process cycle.

periodthe device cycle duration in clock_periods. For example, at 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period was 1.0/44100, or 512/44100 if clock_period was 1.

system_time, in seconds, should be the value of the system clock time, at (or as close as possible to) the moment the device hardware interrupt occurred (or any other event the device clock raises at the beginning of a cycle).

the filtered time, in seconds

Definition at line 72 of file timefilter.c.

Referenced by audio_read_packet(), convert_timestamp(), main(), process_callback(), and pulse_read_packet().

double ff_timefilter_eval ( TimeFilter self,
double  delta 

Evaluate the filter at a specified time.

deltadifference between the requested time and the current time (last call to ff_timefilter_update).
the filtered time

Definition at line 88 of file timefilter.c.

Referenced by convert_timestamp().

void ff_timefilter_reset ( TimeFilter )

Reset the filter.

This function should mainly be called in case of XRUN.

Warning: after calling this, the filter is in an undetermined state until the next call to ff_timefilter_update()

Definition at line 67 of file timefilter.c.

Referenced by audio_read_packet(), and xrun_callback().

void ff_timefilter_destroy ( TimeFilter )

Free all resources associated with the filter.

Definition at line 62 of file timefilter.c.

Referenced by ff_alsa_close(), main(), pulse_close(), and stop_jack().