DSP Blockset

Buffering with Alteration of the Signal.   Some forms of buffering alter the signal's data or sample period, in addition to adjusting the frame size. There are many instances when this type of buffering is desirable, for example when creating sliding windows by overlapping consecutive frames of a signal, or selecting a subset of samples from each input frame for processing.

The blocks that alter a signal while adjusting its frame size are listed below. In this list, T_si is the input sequence sample period, and T_fi and T_fo are the input and output frame periods, respectively.

• Buffer adds duplicate samples to a sequence when the Buffer overlap parameter, L, is set to a nonzero value. The output frame period is related to the input sample period by

• where M_o is the output frame size specified by the Output buffer size (per channel) parameter. As a result, the new output sample period is

• Delay Line adds duplicate samples to the sequence when the Delay line size parameter, M_o, is greater than 1. The output and input frame periods are the same, T_fo = T_fi = T_si, and the new output sample period is

• Variable Selector can remove, add, and/or rearrange samples in the input frame when Select is set to Rows. The output and input frame periods are the same, T_fo = T_fi, and the new output sample period is

• where M_o is the length of the block's output, determined by the Elements vector.

• Zero Pad adds samples to the sequence by appending zeros to each frame when Pad along is set to Columns. The output and input frame periods are the same, T_fo = T_fi, and the new output sample period is

• where M_o is the length of the block's output, determined by the Number of output rows parameter.

In all of these cases, the sample period of the output sequence is not equal to the sample period of the input sequence.

Example: Buffering with Alteration of the Signal.   In the model below, a signal with a sample period of 0.125 second is rebuffered from a frame size of 8 to a frame size of 16 with an overlap of 4.

The relation for the output frame period for the Buffer block is

which indicates that T_fo should be (16-4)*0.125, or 1.5 seconds, as confirmed by the second Probe block. The sample period of the signal at the output of the Buffer block is no longer 0.125 second, but rather 0.0938 second (that is, 1.5/16). Thus, both the signal's data and the signal's sample period have been altered by the buffering operation.

Buffering with Preservation of the Signal

Avoiding Unintended Rate Conversions