Provides a rational resampling filter, which updates the input sample rate by an L/M factor where L is an interpolation factor and M is a decimation factor.

Rational resampling is the process of converting the sample rate of a signal to another sample rate that differs from the original sample rate by a rational factor of L/M, where both L and M are integer values. When L=1 and M>1, the resampling is an integer decimation, and when L>1 and M=1, the resampling is an integer interpolation.

Rational resampling is useful for interfacing with digital signal processing (DSP) systems that operate at different sample rates. By choosing L and M properly, you can approximate any desired sample rate change ratio.


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Dialog Box Options

Parameter Description
Filter Parameters

Contains the following options:

  • L—

    Specifies the interpolation factor.

  • M—

    Specifies the decimation factor.

    Note L and M must never be equal.
  • Stopband attenuation—

    Specifies the attenuation above where the gain versus frequency has finished its rapid falloff. The default is 80 dB.

  • Input sample rate—

    Specifies the sample rate of each input channel. The Input sample rate, combined with L and M, determines the Output sample rate.

  • Output sample rate—

    Indicates the calculated average rate at which the Express VI returns valid output data for each channel.
Implementation

Contains the following options:

  • Show reset terminal—

    Specifies whether this Express VI includes a reset input on the block diagram to reset this Express VI at run time.

  • Number of channels—

    Specifies the number of source channels that this Express VI handles.

  • Adapt to source—

    Specifies whether this Express VI decides the output data type.

    Disable the Adapt to source checkbox if you want to use Word length to determine the output data type.

  • Word length—

    Specifies any output word length in the range of [1, 32]. Word length is available only if you disable the Adapt to source checkbox.

  • Integer word length—

    Indicates the output integer word length that this Express VI calculates.
Filter Response

Displays the actual magnitude response of the filter.
Execution Mode

Contains the following options:

  • Outside single-cycle Timed Loop—

    Select this option to use this Express VI outside of a single-cycle Timed Loop.

    Outside single-cycle Timed Loop is disabled when L/M is greater than 1.
  • Inside single-cycle Timed Loop—

    Select this option to use this Express VI inside a single-cycle Timed Loop.

    Selecting Inside single-cycle Timed Loop enables Throughput. When you execute this Express VI inside the single-cycle Timed Loop, the Express VI provides four handshaking signals you can use to schedule the timing of data. This option is useful if you want to achieve higher throughput using a rational resampling filter.
  • Throughput—

    Displays the minimum number of cycles between two successive frames of valid input data. LabVIEW sets the value of Throughput according to the options you specify in the configuration dialog box.

    Throughput is available only if you select Inside single-cycle Timed Loop. If you select Outside single-cycle Timed Loop, LabVIEW sets the throughput to 1 call / sample, which means that this Express VI can accept data every time it is called.

  • Clock rate—

    Specifies the level of pipelining stages this Express VI uses internally. Increasing the number of stages increases the clock rate at which this Express VI can compile for both Inside the single-cycle Timed Loop and Outside the single-cycle Timed Loop. This option does not set the clock rate explicitly. <note>Note  Adjusting the value of Clock rate increases the FPGA resource usage and latency of this Express VI. An increased latency indicates that this Express VI takes longer to return a valid result.</note>
Configuration Feedback

Displays information about how this Express VI executes. This information is based on the configuration options you specify. LabVIEW displays this information only if you select Outside single-cycle Timed Loop.

Inputs/Outputs

  • cunkn.png input data —

    Specifies the data you want to filter.

  • reset —
    Resets the state of the internal resampling filter.Outside the single-cycle Timed Loop, the Express VI restarts on the same call that reset is TRUE. Inside the single-cycle Timed Loop, the Express VI restarts on the first call that reset is deasserted after reset is TRUE. Additionally, the handshaking signals behave as follows during the cycles where reset is asserted:
    • input valid is ignored.
    • ready for output is ignored.
    • output valid is FALSE.
    • ready for input is FALSE, which handles cases where reset is held TRUE for a long time. The Express VI is not ready for inputs when reset is asserted.
  • input valid —

    Specifies whether the next data point has arrived for processing. Wire the output valid output of an upstream node to this input to transfer data from the upstream node to this node.

    To display this handshaking terminal, select Inside single-cycle Timed Loop in the configuration dialog box.

  • ready for output —

    Specifies whether downstream nodes are ready for this Express VI to return a new value. The default is TRUE. Use a Feedback Node to wire ready for input of a downstream node to ready for output of the current node.

    Note If ready for output is FALSE during a given cycle, output valid returns FALSE during that cycle.

    To display ready for output, select Inside single-cycle Timed Loop in the configuration dialog box.

  • iunkn.png output data —

    Returns the filtered data.

  • ibool.png output valid —

    Returns TRUE if this node has computed a result that downstream nodes can use. Wire this output to the input valid input of a downstream node to transfer data from the node to the downstream node.To display output valid, select Inside single-cycle Timed Loop in the configuration box.

  • ready for input —

    Returns TRUE if this node is ready to accept new input data. Use a Feedback Node to wire ready for input to ready for output of an upstream node.

    Note If ready for input is FALSE during a given cycle, LabVIEW discards any data that other nodes send to this Express VI during the following cycle. LabVIEW discards this data even if input valid is TRUE during the following cycle.

    To display ready for input, select Inside single-cycle Timed Loop in the configuration dialog box.

  • iu8.png channel index —

    Indicates the index of the channel corresponding to the last valid output data.

    • This Express VI supports handshaking with multiple channels.