Upsample (DSP Blockset)

Resample an input at a higher rate by inserting zeros.

Library

Signal Operations, in General DSP

Description

The Upsample block resamples the discrete input at a rate L times faster than the input sample rate by inserting L-1 zeros between consecutive samples, where L is the integer Upsample factor. The Sample offset delays the output samples by an integer number of sample periods D (D<L), so that any of the L possible output phases can be selected.

The Frame-based inputs parameter allows you to choose between sample-based and frame-based operation.

Sample-Based Operation

When the check box is not selected (default), the block assumes that the input is a 1-by-N sample vector or M-by-N sample matrix. Each of the N vector elements (or M*N matrix elements) is treated as an independent channel, and the block upsamples each channel over time. The output sample rate is L times higher than the input sample rate, and the input and output sizes are identical.

In sample-based mode, the Initial condition can be a vector of length N (length M*N for a matrix input) containing one value for each channel, or a scalar to be applied to all signal channels. This value is output at t=D.

Frame-Based Operation

When the Frame-based inputs check box is selected, the block assumes that the input is an M-by-N frame matrix. Each of the N frames in the matrix contains M sequential time samples from an independent signal. The illustration below shows a 6-by-4 matrix input:

The Number of channels parameter specifies the number of independent channels (columns, N) in the matrix. Frame-based operation provides substantial increases in throughput rates, at the expense of greater model latency.

In frame-based operation, the block upsamples each channel independently by inserting L rows of zeros between each row in the original input matrix. The Framing parameter determines how the block adjusts the rate at the output. There are two available options:

Maintain input frame size

The block generates the output at the faster (upsampled) rate by using a proportionally shorter frame period at the output port than at the input port. For upsampling by a factor of L, the output frame period is L times shorter than the input frame period, but the input and output frame sizes are equal.

The example below shows a single-channel input with a frame period of 1 second (Sample time = 1/64 and Samples per frame = 64 in the Signal From Workspace block) being upsampled by a factor of 4 to a frame period of 0.25 seconds. The input and output frame sizes are identical.

Maintain input frame rate

The block generates the output at the faster (upsampled) rate by using a proportionally larger frame size than the input. For upsampling by a factor of L, the output frame size is L times larger than the input frame size, but the input and output frame rates are equal.

The example below shows a single-channel input of frame size 16 being upsampled by a factor of 4 to a frame size of 64. The input and output rates are identical.

In frame-based mode, the Initial condition can be an M-by-N matrix representing the initial input, or a scalar to be repeated across all elements of the M-by-N matrix. The first row of the matrix is output at t=D, where D is the Sample offset.

Dialog Box

Upsample factor: The integer factor, L, by which to increase the input sample rate.
Sample offset: The sample offset, D, which must be an integer in the range [0,L-1].
Initial condition: The value that the block is initialized with; a scalar or vector in sample-based mode, or a scalar or matrix in frame-based mode. This value (first row in frame-based mode) is output at t=D.
Frame-based inputs: Selects frame-based operation.
Number of channels: For frame-based operation, the number of columns (frames) in the input matrix.
Framing: For frame-based operation, the method by which to implement the upsampling: increase the output sample rate, or increase the output frame size.