TimeDelay

class baseband.tasks.TimeDelay(ih, delay, *, lo, frequency=None, sideband=None)

Bases: baseband_tasks.base.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 with shift as the delay, no offset, and pad=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.

loQuantity, or None

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 in None.

frequencyQuantity, 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.

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

closed
complex_data
dtype	Data type of the output.
meta
ndim	Number of dimensions of the output.
offset
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.
shape	Shape of the output.
size	Number of component samples in the output.
start_time	Start time of the output.
stop_time	Time at the end of the output, just after the last sample.
time	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.

start_time

Start time of the output.

See also time and stop_time.

stop_time

Time at the end of the output, just after the last sample.

See also start_time and time.

time

Time of the sample pointer’s current offset in the output.

See also start_time and stop_time.

Methods Documentation

close()

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)

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 if out 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 equal sample_shape.

Returns

outndarray of float or complex

The first dimension is sample-time, and the remaining ones are as given by sample_shape.

seek(offset, whence=0)

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, or Time

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 if offset is a time.

task(data)

tell(unit=None)

Current offset in the file.

Parameters

unitUnit 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.

Returns

offsetint, Quantity, or Time

Offset in current file (or time at current position).