TimeDelay¶
- class baseband.tasks.TimeDelay(ih, delay, *, lo, frequency=None, sideband=None)[source] [edit on github]¶
Bases:
TaskBase
Delay a stream by a given amount, taking care of phase rotations.
The delay is added to the sample times (by adding to the
start_time
of the stream), and the sample phases are rotated as needed if the signal was recorded after mixing with a local oscillator. For an upper sideband, the phases are rotated by\[\phi = - \tau f_{lo}.\]For the lower sideband, the rotation is in the opposite direction.
Note that the input data stream must be complex. For real-valued streams, use
ShiftAndResample
withshift
as the delay, nooffset
, andpad=0
(this works for complex data as well, but is slower as it involves fourier transforms).- Parameters:
- ihtask or
baseband
stream reader Input data stream, with time as the first axis.
- delayfloat,
Quantity
Delay to apply to all times. Can be (float) samples, or a quantity with units of time.
- lo
Quantity
, orNone
Local oscillator frequency. For raw data, this can just be
if.frequency
. But for channelized data, the actual frequency needs to be passed in. If data were recorded without mixing (like for CHIME), pass inNone
.- frequency
Quantity
, optional Frequencies for each channel. Should be broadcastable to the sample shape. By default, taken from the underlying stream. (Note that these frequencies are not used in the calculations here.)
- sidebandarray, optional
Whether frequencies are upper (+1) or lower (-1) sideband. Should be broadcastable to the sample shape. By default, taken from the underlying stream. Assumed to be correct for the lo.
- ihtask or
See also
ShiftAndResample
also resample a stream, or delay a real-valued stream
baseband_tasks.base.SetAttribute
change start time without phase delay
Attributes Summary
Data type of the output.
Number of dimensions of the output.
Number of complete samples per second.
Shape of a complete sample.
Number of samples per frame of data.
Shape of the output.
Number of component samples in the output.
Start time of the output.
Time at the end of the output, just after the last sample.
Time of the sample pointer's current offset in the output.
Methods Summary
close
()Close task.
read
([count, out])Read a number of complete samples.
seek
(offset[, whence])Change the sample pointer position.
task
(data)tell
([unit])Current offset in the file.
Attributes Documentation
- closed = False¶
- complex_data¶
- dtype¶
Data type of the output.
- meta¶
- ndim¶
Number of dimensions of the output.
- offset = 0¶
- sample_rate¶
Number of complete samples per second.
- sample_shape¶
Shape of a complete sample.
- samples_per_frame¶
Number of samples per frame of data.
For compatibility with file readers, to help indicate what a nominal chunk of data is.
- shape¶
Shape of the output.
- size¶
Number of component samples in the output.
- stop_time¶
Time at the end of the output, just after the last sample.
See also
start_time
andtime
.
- time¶
Time of the sample pointer’s current offset in the output.
See also
start_time
andstop_time
.
Methods Documentation
- close() [edit on github]¶
Close task.
Note that this does not explicitly close the underlying source; instead, it just deletes the reference to it.
- read(count=None, out=None) [edit on github]¶
Read a number of complete samples.
- Parameters:
- countint or None, optional
Number of complete samples to read. If
None
(default) or negative, the number of samples left. Ignored ifout
is given.- outNone or array, optional
Array to store the samples in. If given,
count
will be inferred from the first dimension; the remaining dimensions should equalsample_shape
.
- Returns:
- out
ndarray
of float or complex The first dimension is sample-time, and the remaining ones are as given by
sample_shape
.
- out
- seek(offset, whence=0) [edit on github]¶
Change the sample pointer position.
This works like a normal filehandle seek, but the offset is in samples (or a relative or absolute time).
- Parameters:
- offsetint,
Quantity
, orTime
Offset to move to. Can be an (integer) number of samples, an offset in time units, or an absolute time. For the latter two, the pointer will be moved to the nearest integer sample.
- whence{0, 1, 2, ‘start’, ‘current’, or ‘end’}, optional
Like regular seek, the offset is taken to be from the start if
whence=0
(default), from the current position if 1, and from the end if 2. One can alternativey use ‘start’, ‘current’, or ‘end’ for 0, 1, or 2, respectively. Ignored ifoffset
is a time.
- offsetint,
- task(data)[source] [edit on github]¶
- tell(unit=None) [edit on github]¶
Current offset in the file.
- Parameters:
- unit
Unit
or str, optional Time unit the offset should be returned in. By default, no unit is used, i.e., an integer enumerating samples is returned. For the special string ‘time’, the absolute time is calculated.
- unit
- Returns: