diff options
| -rw-r--r-- | nncmpp.c | 13 |
1 files changed, 11 insertions, 2 deletions
@@ -769,9 +769,18 @@ spectrum_init (struct spectrum *s, char *format, int bars, struct error **e) // Discard frequencies above 20 kHz, which take up a constant ratio // of all bins, given by the sampling rate. A more practical/efficient - // solution would be to just handle 96/192/... kHz as bitshifts. + // solution would be to just handle 96/192/... kHz rates as bitshifts. // - // Trying to filter out sub-20 Hz frequencies would be even more wasteful. + // Filtering out sub-20 Hz frequencies would be even more wasteful than + // this wild DFT size, so we don't even try. While we may just shift + // the lowest used bin easily within the extra range provided by this + // extension (the Nyquist is usually above 22 kHz, and it hardly matters + // if we go a bit beyond 20 kHz in the last bin), for a small number of bars + // the first bin already includes audible frequencies, and even for larger + // numbers it wouldn't be too accurate. An exact solution would require + // having the amount of bins be strictly a factor of Nyquist / 20 (stemming + // from the equation 20 = Nyquist / bins). Since log2(44100 / 2 / 20) > 10, + // it would be fairly expensive, and somewhat slowly updating. Always. double audible_ratio = s->sampling_rate / 2. / 20000; s->bins = ceil (necessary_bins * MAX (audible_ratio, 1)); s->useful_bins = s->bins / 2; |