Waveform View becomes "pixelated" [Audacity 2.0.6]

[Gunnar]

Hello.

Is it normal that the Waveform view in Audacity becomes "pixelated" when I use the horizontal slider (scrollbar) to go forth and back a few times?

This is how it looks right after opening the file:
http://i.imgur.com/TXOLLHn.png

And this is how it looks after using the horizontal slider a few times:
http://i.imgur.com/MSAoVJd.png

IMO this looks a bit strange. Tested with Audacity 2.0.6 RC, tested on Windows 7 (x64).

Regards.

[kozikowski]

Does it do that in 2.0.5, the current version?
Koz

[Gunnar]

Does it do that in 2.0.5, the current version?
Koz

I just "downgraded" to version 2.0.5. And yes, it does show the same strange "pixelation" effect.

[Gale Andrews]

You mean, you just drag on the horizontal scrollbar, nothing else?

Do you have any other computers you could test on?


Gale

[Gunnar]

You mean, you just drag on the horizontal scrollbar, nothing else?

Exactly.

Do you have any other computers you could test on?

Yes, I can test on my Laptop, running on Windows 8, x64. Will report back later...

[kozikowski]

I've never heard of Audacity doing that, so I predict the other machine will work fine and it will turn out to be a video/graphics management problem on that one.

Koz

[Gunnar]

it will turn out to be a video/graphics management problem on that one.

I don't think so. I use a fully-patched Windows 7 SP-1 with a GeForce GTX 660 Ti graphics card and latest ForceWare (WHQL) drivers. Not exactly an unusual configuration, I think.

Anyway, I will check this under Windows 8.1 on my laptop now...

[Gunnar]

Okay, it apparently does not happen on my Windows 8.1 laptop. I can also check on my Windows 7 machine at work, but not before Thursday...

[Gunnar]

Okay, it apparently does not happen on my Windows 8.1 laptop. I can also check on my Windows 7 machine at work, but not before Thursday...

I have been able to test on my Windows 7 machine at work today. And it didn't show the problem either. So this problem remains a bit of a mystery

Two differences between my "main" machine, which shows the problem, and the other two (laptop + machine at work), which do not show the problem, are: The "main" machine has two screens with "full hd" resolution, while my laptop and my machine at work have only a single screen each (and with lower resolution). Furthermore, my "main" machine uses a dedicated graphics card (GeForce GTX 660 Ti), while the other two use Intel "on board" graphics.

Unfortunately, I have no other machine that has a dedicated graphics card and is connected with two "full hd" screens...

[steve]

When Audacity draws the waveform, the image data is temporarily stored in memory so that it can be retrieved quickly with minimal load on the processor. The waveform is therefore only redrawn when necessary, thus improving overall performance. If the audio data is changed, then the waveform has to be redrawn (often this takes as much time as processing the audio, which is why redrawing is avoided when possible).

Another case where the waveform is redrawn is when there is a substantial change in the zoom level.
When zoomed out a long way, the waveform is drawn based on calculations that take an appropriate amount of detail.
When zooming in much closer, the waveform needs to be redrawn so as to show extra detail. In this case Audacity will probably not draw the entire waveform, just a bit more than shows on screen.

What I guess is happening, is that your high performance dedicated graphics card is also doing its own caching. (Running two Hi Def monitors requires a huge amount of data). Unfortunately it seems that your graphics card is not quite "smart enough", and can be tricked (by rapid scrolling) to hold old cache data longer than it should, and so sometimes display low resolution (pixelated) waveform data rather than the most recent waveform data. A driver update for your graphics card (if available) may solve the problem, or making less demands on the card (for example, running only one monitor, or using lower definition, or a lower refresh rate).