Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>This is a difficult problem, requiring more than an FFT. I'll briefly describe how I implemented beat detection when I was writing software for professional DJ equipment.</p> <p>First of all, you'll need to cut down the amount of data you're dealing with, since there are only two or three beats per second, but tens of thousands of samples. You'll also need to look at different frequency ranges, since some types of music carry the tempo in the bassline, and others in percussion or other instruments. So pass the signal through several band-pass filters (I chose 8 filters, each covering one octave, from low bass to high treble), and then downsample each band by averaging the power over a few hundred samples.</p> <p>Every few seconds, you'll have a thousand or so samples in each band. Your next tool is an autocorrelation, to identify repetitive patterns in the music. The peaks of the autocorrelation tell you what the beat is more or less likely to be; but you'll need to make up some heuristics to compare all the frequency bands to find a beat that you can be confident in, and to avoid misleading syncopations. If you can manage that, then you'll have a reasonable guess at the tempo, but no idea of the phase (i.e. exactly when to flash the screen).</p> <p>Now you can look at the a smoothed version of the audio data for peaks, some of which are likely to correspond to beats. Initially, look for the strongest peak over the course of a few seconds and take that as a downbeat. In conjunction with the tempo you estimated in the first stage, you can predict when the next beat is due, and measure where you actually saw something like a beat, and adjust your estimate to more closely match the data. You can also maintain a confidence level based on how well the predicted beats match the measured peaks; if that drops too low, then restart the beat detection from scratch.</p> <p>There are a lot of fiddly details to this, and it took me some weeks to get it working nicely. It is a difficult problem.</p> <p>Or for a simple visualisation effect, you could simply detect peaks and flash the screen for each one; it will probably look good enough.</p>
    singulars
    1. This table or related slice is empty.
    1. POHelp with FFT(Fast Fourier Transforms) and/or DSP
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USMike Seymour
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHelp with FFT(Fast Fourier Transforms) and/or DSP
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COAnd how do I detect the peaks?
      singulars
      1. PO
      1. USSismetic
    2. CO@Sismetic: One simple way is to keep track of the average amplitude, and look for samples that are both considerably larger than average, and larger than all other samples within a smallish distance (say 100ms) of them. You might get better results by rectifying the signal (making negative samples positive), smoothing it (with a low-pass filter) and looking for attacks (sudden increases in amplitude), but that's more complicated.
      singulars
      1. PO
      1. USMike Seymour
    3. COAnd how do I get the samples?Sorry Im a REAL newbie
      singulars
      1. PO
      1. USSismetic
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload