[linux-audio-dev] Waveform

Fred Gleason fredg at salemradiolabs.com
Mon May 9 23:29:44 UTC 2005

On Monday 09 May 2005 19:02, Paul Davis wrote:

> if you allow arbitrary zoom scales, then the mapping between pixel
> position on screen (or some notional "unit" position as offered by
> canvas widgets) and a sample is non-integral, which implies
> rounding. that in turn implies errors of several different kinds.
> moreover, if you are displaying large audio files, reading the audio
> data itself is excrutiatingly slow. hence, peakfiles.

And here's another one in Qt, from Rivendell's Marker Editor:


Unpack the tarball and look in rdlibrary/edit_audio.cpp.

Paul is quite right about all the round-off and peak-file issues.  Rivendell 
handles that by assuming that the smallest atom of audio is always 1152 
samples long -- which just happens to be the standard MPEG sample block size.  
This gives acceptable precision for the marker editor, but would probably not 
be adequate in a general purpose editor.  Even the 'simplified' version is 
quite headache-inducing enough, however...  :)


| Frederick F. Gleason, Jr. | Director of Broadcast Software Development  |
|                           |             Salem Radio Labs                |
|    Never worry about theory as long as the machinery does what it's     |
|    supposed to do.                                                      |
|                                         -- Robert A. Heinlein           |

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