Convert a 1D signal x into overlapping windows of width `frame_width` using a hop length of `stride`. Notes ----- If ``(len(x) - frame_width) % stride != 0`` then some number of the samples in x will be dropped. Specifically:: n_dropped_frames = len(x) - frame_widt
(x, frame_width, stride, writeable=False)
| 352 | |
| 353 | |
| 354 | def to_frames(x, frame_width, stride, writeable=False): |
| 355 | """ |
| 356 | Convert a 1D signal x into overlapping windows of width `frame_width` using |
| 357 | a hop length of `stride`. |
| 358 | |
| 359 | Notes |
| 360 | ----- |
| 361 | If ``(len(x) - frame_width) % stride != 0`` then some number of the samples |
| 362 | in x will be dropped. Specifically:: |
| 363 | |
| 364 | n_dropped_frames = len(x) - frame_width - stride * (n_frames - 1) |
| 365 | |
| 366 | where:: |
| 367 | |
| 368 | n_frames = (len(x) - frame_width) // stride + 1 |
| 369 | |
| 370 | This method uses low-level stride manipulation to avoid creating an |
| 371 | additional copy of `x`. The downside is that if ``writeable`=True``, |
| 372 | modifying the `frame` output can result in unexpected behavior: |
| 373 | |
| 374 | >>> out = to_frames(np.arange(6), 5, 1) |
| 375 | >>> out |
| 376 | array([[0, 1, 2, 3, 4], |
| 377 | [1, 2, 3, 4, 5]]) |
| 378 | >>> out[0, 1] = 99 |
| 379 | >>> out |
| 380 | array([[ 0, 99, 2, 3, 4], |
| 381 | [99, 2, 3, 4, 5]]) |
| 382 | |
| 383 | Parameters |
| 384 | ---------- |
| 385 | x : :py:class:`ndarray <numpy.ndarray>` of shape `(N,)` |
| 386 | A 1D signal consisting of N samples |
| 387 | frame_width : int |
| 388 | The width of a single frame window in samples |
| 389 | stride : int |
| 390 | The hop size / number of samples advanced between consecutive frames |
| 391 | writeable : bool |
| 392 | If set to False, the returned array will be readonly. Otherwise it will |
| 393 | be writable if `x` was. It is advisable to set this to False whenever |
| 394 | possible to avoid unexpected behavior (see NB 2 above). Default is False. |
| 395 | |
| 396 | Returns |
| 397 | ------- |
| 398 | frame: :py:class:`ndarray <numpy.ndarray>` of shape `(n_frames, frame_width)` |
| 399 | The collection of overlapping frames stacked into a matrix |
| 400 | """ |
| 401 | assert x.ndim == 1 |
| 402 | assert stride >= 1 |
| 403 | assert len(x) >= frame_width |
| 404 | |
| 405 | # get the size for an element in x in bits |
| 406 | byte = x.itemsize |
| 407 | n_frames = (len(x) - frame_width) // stride + 1 |
| 408 | return as_strided( |
| 409 | x, |
| 410 | shape=(n_frames, frame_width), |
| 411 | strides=(byte * stride, byte), |
no outgoing calls