Functions
TimeFilter *	ff_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

◆ ff_timefilter_new()

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.

Parameters

time_base	period of the hardware clock in seconds (for example 1.0/44100)
period	expected update interval, in input units
brandwidth	filtering bandwidth, in Hz

Returns: 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().

◆ ff_timefilter_update()

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.

Parameters

period the 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).