Annoying problem when changing playback spead

[Thunderbolt1000T]

I have several long files that were recorded on portable digital recorders. I've tried changing the playback speed to skim through the files, but when I get to a part I want to edit, and change the spead back to normal, it unselects everything I've selected, and moves the cursor back to 0000. What do I do to fix this annoying problem?

[Gale Andrews]

I have several long files that were recorded on portable digital recorders. I've tried changing the playback speed to skim through the files, but when I get to a part I want to edit, and change the spead back to normal, it unselects everything I've selected, and moves the cursor back to 0000. What do I do to fix this annoying problem?

We wouldn't know, because you haven't described how you are navigating along, how you are selecting places to edit and how you changed the speed back to normal. Basically if you draw a selection and click, it destroys the selection. If you press Stop or Space to stop playback, then press the normal Play button, play starts from the last point you started playback from. If you press |<< it skips to the start and destroys the selection.

You can use CTRL + M to add a label at the playback cursor. To create a selection while playing, drag it out on the waveform, or use [ to mark the start of a selection at the current playback point and ] to mark the end of that selection at the current playback point. Then CTRL + B to label the selection. Click in the label to recall the point or selection at any time.

If you want to stop at a point and restart from there, use SHIFT + A to set the cursor at the place you stopped.

See Navigation Tips for more hints like this.



Gale

[Thunderbolt1000T]

Here's an update. I experimented with it, and I got one problem fixed, only to find another. When I'm playing at the highest spead available in 1.3.7, 300 percent, I find the point at which I want to edit or listen at normal spead, and use [ to select the starting point (shift+a doesn't work in 1.3.7.) I press the space bar twice to play the audio at normal spead. When I'm ready to start skimming again, I move the spead slider back to 300 percent, but instead of just changing the spead, it restarts the audio at the point I selected before I hit the space bar twice in the step above. Every time I move the spead slider, the audio restarts at that point. It's very annoying. Why doesn't it just keep playing the audio without restarting when I change the spead?

BTW, are there any plugins or updates available that can allow me to play the audio at speads higher than 300 percent?

[steve]

Audacity 1.3.7 is an old version - it is highly recommended that you update. The current version is 1.3.12

(shift+a doesn't work in 1.3.7.)

It works in Audacity 1.3.12

If you want to play faster than 300% you can temporarily change the track sample rate - Click on the name of the track and from the drop down menu select "Set Rate". Select a higher rate for faster playback (the maximum supported rate is 200kHz).
To revert to normal speed, set the rate back to whatever it was initially.
This can be used in conjunction with the Transcription slider.

[Gale Andrews]

When I'm playing at the highest spead available in 1.3.7, 300 percent, I find the point at which I want to edit or listen at normal spead, and use [ to select the starting point (shift+a doesn't work in 1.3.7.) I press the space bar twice to play the audio at normal spead. When I'm ready to start skimming again, I move the spead slider back to 300 percent, but instead of just changing the spead, it restarts the audio at the point I selected before I hit the space bar twice in the step above. Every time I move the spead slider, the audio restarts at that point. It's very annoying. Why doesn't it just keep playing the audio without restarting when I change the spead?

Whenever you change the playback speed Audacity currently needs to restart playback, and playback always restarts from the cursor. It's logged as Bug 235 that if you change speed during playback, playback should restart from the playback position it stops at.

Unfortunately 1.3.12 has an additional problem compared to 1.3.7 that moving the Play-at-speed slider during play has no effect - you have to click the Play-at-speed button again to restart playback at the new speed (from the start position of the cursor).


Gale

[Thunderbolt1000T]

Steve, before I update to 1.3.12, I have some questions. I use Fredom Scientific JAWS screen reader, and most features of 1.3.5 and 1.3.7 work, but do you know whether JAWS will work with 1.3.12? Also, do I need to uninstall the old version before or after updating? Also, about changing the rate, in earlier versions, if I selected audio, then changed the rate, the track would start back at 00:00, regardless of where the selection start was. Does 1.3.12 do the same thing? One more thing, what other featurs does 1.3.12 hve besides a better compressor effect and the bass cut effect?

[steve]

do you know whether JAWS will work with 1.3.12

Yes it should, but please report any problems, particularly anything that worked in previous versions but no longer works.

do I need to uninstall the old version before or after updating?

No you don't. If you installed the previous version in the default location than the new version will install over the top. In effect it will update your current version and previous settings will be retained. If you have problems an need to revert back to 1.3.7 you just need to re-run the 1.3.7 installer.

in earlier versions, if I selected audio, then changed the rate, the track would start back at 00:00, regardless of where the selection start was. Does 1.3.12 do the same thing?

If you change the rate using the track drop down menu, then the start position stays at the same absolute time. So if the playback cursor was at 3:00, then it will stay at 3:00, but this will of course correspond to a different position in the audio.
I don't think there is any way to maintain the same position in the audio.

Also, as you use Jaws it occurs to me that you may not be a mouse user, and I'm not sure if the track drop-down menu is accessible via the keyboard. If you are able to access this menu perhaps you could tell me how (this menu contains "Move Track Up, Move Track Down, Waveform, Waveform dB, Spectrum, Spectrum log f" and other options. It is not the "Tracks" menu in the main menu bar.) If you are not able to access this menu, I'll try to find out if there is a way to do so.

what other featurs does 1.3.12 hve besides a better compressor effect and the bass cut effect?

There are many bug fixes and other enhancements - too many to list here. See here for the list of changes: http://audacityteam.org/download/features-1.3-a

[Gale Andrews]

If you change the rate using the track drop down menu, then the start position stays at the same absolute time. So if the playback cursor was at 3:00, then it will stay at 3:00, but this will of course correspond to a different position in the audio. I don't think there is any way to maintain the same position in the audio.

If you need to retain the selection or cursor point relative to its original position before you sped up, in 1.3.12 you can label the selection or cursor with CTRL + B, then run Effect > Change Speed on the whole audio track, including the label track in the selection. If the label track is not selected, down arrow to give it focus, then hit ENTER. The label will then move after Change Speed, retaining its relative position. To select the label and recall the selection or cursor point it relates to, down arrow to give the label track focus, then TAB to select the label.

A downside is that to undo the Change Speed when you want to export at the real speed, you need to work out the maths to slow down the track to original speed (for example, a 100% speed change will halve the track length/double the playback speed, but to restore the original track length/speed you need a -50% change). There is also a possible "loss of frequency bandwidth" downside if you speed up using Change Speed then revert it by slowing down - see below discussion.

I'm not sure if the track drop-down menu is accessible via the keyboard.

Yes it is - the shortcut to open the menu on the focused track is SHIFT + M. You can read the default keyboard shortcuts for 1.3.12 in the Manual. Also read David Bailes' Guide to using Audacity with JAWS - it's still at 1.3.11 but still mostly relevant.



Gale

[steve]

The only downside is that to undo the Change Speed when you want to export at the real speed, you need to work out the maths to slow down the track to original speed (for example, a 100% speed change will halve the track length/double the playback speed, but to restore the original track length/speed you need a -50% change).

There is another downside which is that this method works by resampling, which is a lossy process. Increasing the speed by 100% then reducing back by 50% will reduce the frequency bandwidth by 50%, so if the track has a sample rate of 44100 Hz, the available bandwidth before the process is about 20 kHz, but after the conversion the upper frequency limit is about 10 kHz. Any sound above 11 kHz is totally lost.

Yes it is - the shortcut to open the menu on the focused track is SHIFT + M.

Thanks Gale. I'm having a lot of trouble getting shortcuts to work on Linux. Sometimes the tracks just don't get highlighted (yellow border), so the track shortcuts don't work, and I don't yet know why they sometimes work and sometimes don't.

[Gale Andrews]

The only downside is that to undo the Change Speed when you want to export at the real speed, you need to work out the maths to slow down the track to original speed (for example, a 100% speed change will halve the track length/double the playback speed, but to restore the original track length/speed you need a -50% change).

There is another downside which is that this method works by resampling, which is a lossy process. Increasing the speed by 100% then reducing back by 50% will reduce the frequency bandwidth by 50%, so if the track has a sample rate of 44100 Hz, the available bandwidth before the process is about 20 kHz, but after the conversion the upper frequency limit is about 10 kHz. Any sound above 11 kHz is totally lost.

Quite a downside indeed, should have thought of that. And come to mention it, it's quite a common mistake to use Change Speed without realising Change Tempo doesn't affect pitch or frequency range. So I added that to the "Intro" for the "Change Speed" entry in the Manual.

Someone may jump in and point out that reducing the sample rate in "Change Rate" also removes the high frequencies, even though it is not resampling but only changing the rate the samples are being "pushed out" at (Is there a better description than that)?

So I guess we should explain the reason you can use "Change Rate" to increase the rate and then reduce it without losing the original range of frequencies is that increasing the rate always proportionally increases the higher frequencies that can be carried (increases the bandwidth). Resampling on the other hand cannot (to oversimplify) increase the higher frequencies in the audio beyond half the sample rate of the track. So in an audio track at a sample rate of 44100 Hz, however much you speed up the audio using Change Speed, you cannot increase the highest frequency it contains above 22050 Hz. However if your original audio did not have frequencies above 11025 Hz (as with speech), you "could" Effect > Change Speed +100% followed by - 50% without losing the original frequency range.

I suppose this raises an interesting question if you want to reduce pitch and tempo, do you do it the "natural" way with Change Speed and risk losing high frequencies, or with Change Tempo followed by Change Pitch (or with Sliding Time Scale), and keep the frequency bandwidth but risk artifacts from the stretching?

I'm having a lot of trouble getting shortcuts to work on Linux. Sometimes the tracks just don't get highlighted (yellow border), so the track shortcuts don't work, and I don't yet know why they sometimes work and sometimes don't.

FWIW I am not seeing that on Ubuntu 10.10. Is this after previewing or applying an effect, or opening a dialogue like Preferences? Something like that has happened several times on Mac and Linux over the years.



Gale