User`s guide

Sample Rates and Frame Rates
3-21
•Direct rate conversions
Direct rate conversions, such as upsampling and downsampling, are a
feature of most DSP systems, and can be implemented by altering either the
frame rate or the frame size of a signal.
•Frame rebuffering
The principal purpose of frame rebuffering is to alter the frame size of a
signal, usually to improve simulation throughput. By redistributing the
signal samples to frames of a new size, rebuffering usually changes either
the sample rate or frame rate of the signal.
Both operations are discussed in the following sections, along with ways to
avoid unintentional rate conversions:
•“Direct Rate Conversion”
•“Frame Rebuffering”
•“Avoiding Unintended Rate Conversions”
You may also want to look at the Sample Rate Conversion demo,
dspsrcnv.mdl.
Note Technically, when a Simulink model contains signals with various
frame rates, the model is called multirate. You can find a discussion of
multirate models in “Delay and Latency” on page 3-85 and in the “Discrete
Time Systems” section of the Simulink documentation.
Direct Rate Conversion
Rate conversion blocks accept an input signal at one sample rate, and
propagate the same signal at a new sample rate. Several of these blocks contain
a
Frame-based mode parameter offering two options for adjusting the sample
rate of the signal:
•
Maintain input frame rate: Change the sample rate by changing the frame
size (i.e., M
o
≠ M
i
), but keep the frame rate constant (i.e., T
fo
=T
fi
)
•
Maintain input frame size: Change the sample rate by changing the output
frame rate (i.e., T
fo
≠ T
fi
), but keep the frame size constant (i.e., M
o
= M
i
)
The setting of this parameter does not affect sample-based inputs.