Hi,
I want to make a waveform drawing panel. If i use a zoomed out look of the wave it doesn't seems to be the correct output like audio editors use. If the wave is zoomed out , for example, i paint every eighth point from the samples a line to the next eighth point.
How do audio editor paint the waveform, is there an algorithm?
Thank you,
Thomas
The problem with drawing only 1 in 8 points is that you are
crudely downsampling your data. It is quite possible that you will
miss the high and low points in each 8 point region.
One solution is to alternatley display the highest of the 8 points,
then the lowest. Repeat. More comlpex techniques are possible
but unless you do something like this the overall effect would
appear to reduce the amplitude of the waveform. (not strictly the
case but it would probably look like this was happening.
(depends on the actual data of course)).
matfud
>The problem with drawing only 1 in 8 points is that you are
>crudely downsampling your data. It is quite possible that you will
>miss the high and low points in each 8 point region.
That must be the reason why the wave looks wrong. I read that bevor downsampling you have to filter the
signal with a low pass filter. May be that is a good solution.
>One solution is to alternatley display the highest of the 8 points,
>then the lowest. Repeat. More comlpex techniques are possible
>but unless you do something like this the overall effect would
>appear to reduce the amplitude of the waveform. (not strictly the
>case but it would probably look like this was happening.
>(depends on the actual data of course)).
The data i want to display are audio waveforms. It seems to be an easy solution. May be I can prevent the
problem with the amplitude when I collect the highest and the lowest points representing one point on the
x-axis and draw a line between them.
Thank you for your hints
The problem with using a downsampling filter (a low-pass filter)
is that it remove the high frequencies. This has a similar effect
to just grabbing 1 point in 8. (in fact the attenuation may be far
more pronounced then simply taking 1 in 8 points).
The concept of grabbing the highest then the lowest is also crude
but does give a better visual indication of the amplitude of the
waveform.
Remeber that most wave viwers are not trying to accurately
represent the data, instead they are trying to give the user an
idea of the amplitude. They are also trying to give an idea of the
shape of the wave (but to a lesser extent)
Although as I said in an earlier post the must be better ways
of achieving this then the solution I proposed (which is crude
in the extreme).
matfud