I am stil having a bit of difficulty with mp3 sound player raters.
I would like to record at CD 44KHz and export to mp3s with a bit rate of 40bs. But moodle's flash multimedia plug in plays the mp3 file at double speed.
Michael Penney kindly advised that sampling rates of 22KHz work, and both he David Scotson kindly advised that I change the sample rate using Audacity.
When I halve the sampling rate to 22KHz then both Moodle and a standard MP3 player plays the file at half speed. This is harldly surprising. Halving the sampling rate, while keeping the same number of samples, will halve the speed.
However, when I halve the samping rate and then double the speed, the file plays at the correct speed on other MP3 players, but twice the speed on using the flash multimedia plug in.
Likewise if I double the speed and then half the sampling rater (reversing the order of operations) then the file still plays at teh correct speed on other Mp3 players but at double speed using the flash multimedia plug in.
And just for good measure, I tried halving the speed of the original file too, but that plays at half speed in both the flash mutlimedia player plugin and in other mp3 players.
Hmm...Perhaps I should try changing the speed of the mp3 file after export from audacity, using some other software. No. That did not work either. I doubled the speed of the reduced sample rate mp3 (column) 2 below using wavepad, so that it plays at the right speed in wave pad, but suddenly it plays at double speed in Moodles mp3.
It is very strange.
Please see the table below
Sampling Rate/ Bit Rate / Speed
Speed when playing using moodle multimedia filter
Speed when played using other MP3 players
44KHz / 40bs /normal
22Khz /40bs /normal
22Khz /40bs /double
22Khz /40bs /double
44KHz / 40bs / half
22KHz / 40bs / double
I don't know what other permutations I might try.
Any suggestions on what I might do?
Other players seems to be able to play the files at the right speed, and they are agreeing with each other. If you click the underlined file links in blue you can tests the files in other players. So this seems to be a bug in the flash player. Please can someone tell me who makes it so I can report it?
Phew, I seem to have found an answer. If I export the original 44KHz
Changing the sample rate should not change the speed of the file playback unless the player is expecting a different sample rate from the one the file has.
This might happen because the player is hardcoded to only accept certain sample rates or because the file is contradicting itself by claiming to be a sample rate it is not.
Either way, something odd is going on.
Hello Don McKenzie,
Sorry, I don't understand what you mean by "increase the size"? Perhaps you mean the sample rate?
In my experience, only some combinations of sample rates (when you record) and bit rates (when you export to mp3) work with the audio player that is built in to Moodle, due to the limitations of Macromedia Flash. You will find mention of the correct settings on the forums. The default audacity.org settings (at CD quality 44k i believe) work when you export to 32 or perhaps 40 bps mp3 files.
Dear Don MxKenzie,
Oops, I see now that we are on the same thread as the one where I was talking about the sample and bit rates. You don't like the quality above? I guess it is not ideal but I feel that it is adequate for listening comprehension, maybe. I am more scared of the load on our server than the sound quality.
I think that there is a higher bit rate that one can use with 44k sample rate that does not have the 'chipmonk effect' (I see that this is the term used in the trade). I am asking some about that sample rate now. He or I will get back to you.
With voice recordings I use the following and have no probs at all and fairly small files; before exporting, I always use the Normalize Filter (from Effects), that will increase the quality considerably.
- Quality Tab
Sample rate: 44100 Hz
Sample Format: 16-bit
(set to fast-sync interpolation)
- File format tab
Uncompressed Export Format: 32-bit float
Export Set up Bit Rate: 112
What program are you using to format your audio: audacity? I downloaded it but I also use Goldwave to create audio. I'm willing to try anything to get the size and quality at the 'best'. Thanks!
Wow! Thank you very much... The audio - with the settings you mentioned - sounds great. Now, I'm going to experiment to see which of those settings actually eliminates the 'chipmunk' sound [as apparently we are now officially calling it - and for those searching the forum - it is the audio playing too fast].
I'll update this if I find something of interest or might be helpful to others - beginners like me. Thanks again!
strange happened: the quality is really good but I can only hear a few seconds of the recording. This is with Firefox. With IExplorer it doesn't work at all. Of course, this might not have anything to do with the bitrate. Has anybody else experienced something similar?
I am asking some about that sample rate now. He or I will get back to you.
I guess that would be me...
I do not post a lot of audio files on my site, so I have not had to worry too much about file size at this point. The files are never streamed concurrently either, so the load on the server is not an issue for me. As such, I do not compress my audio files a great deal. Most of the files on my site are sampled at 44.1kHz and exported with a bit rate of 128. This gives me roughly a 1 MB/minute file size ratio.
I have used both Audacity and iTunes to export these files. I often just use iTunes, as it is my default CD ripper, and it just works. I have toyed with the bit rates, and I have yet to run into anything that sounds like Alvin and his pals. I have not documented my experiments as well as Timothy, but I haven't any problems yet.
As I plan to use more audio files in the coming semester, perhpas I will experiment a bit the the rates to see how iTunes fares...
I just uploaded two more attempt at 24 and 40 bits, once again from the original 128 bit file. They worked just fine as well...
Maybe I will run the same series of conversions with Audacity tomorrow to see if I have the same results.
As long as you use 44Khz, 22Khz or 11Khz then Macromedia Flash (which contains the MP3 routines that our player uses) will play your MP3 at the default speed. None of the other parameters matter.
I know this is not the forum to come to. But I have encountered some problems in the enrolment links.
You can go to this discussion to find out more. Iam not sure if it is a bug.
thanks if you could look into this.
I thought that your answer above was going to the be answer to all my confusion - just export using 11, 22 or 44.
But I find that audacity does not seem to export using any of those bit rates three bit rates. Please see the screen capture below.
And at the same time, I think that I have successfully created files for moodle using audacity.
So I am still somewhat confused.
Anyway, after trying various speeds, it seems that 32bs works
I notice that I had worked that out before...rediscovering the wheel.
The 44.1Khz, 22Khz or 11Khz references refer to the sampling rates that have historically been used to sample analog files for digital recording (when CD's first became widespread most mastering was still analog, so an analog master would be digitally sampled for recording as a CD). The resulting digital sound file would then be recorded in multiples of eight bits per second (eight, sixteen, twenty-four, thirty-two) according to the number of outputs on the A/D and D/A converters used. As an MP3 file is already in digital form, there is no need for a sampling stage, so a rough idea of the quality can be given by the bits per second (the sound quality depends on many additional factors, such as cut-off frequencies of filters at the time of inputting the speech etc.). The scale shown above is simply the number of bits per second increasing in various multiples of eight. 32 bits per second should be more than adequate for speech in most cases.
Thanks for digging up the Georgian language bug by the way. I haven't had time to work on it yet but my hopes are high (as usual ).
Yes, I misunderstood Martin. But I misunderstood because it is not just a question of using 44.1Khz, 22Khz or 11Khz. Only some bit rates play at the right speed. I am not sure why or which ones, but some bit rates play like a chipmunk. Any ideas as to why?
Audacity is less than straightforward when it comes to this stuff. In fact I just tried it and it seems to be quietly dropping sample rates on the fly when low bitrates are chosen!! This must be your problem. Shoot for one of the combinations above and when you get a functional Audacity workflow, stick with it!
Are the one's that are playing at the right speed something along the lines of 16, 32, 64, 128, or are they just random? And did Martin use this as a sly opportunity to get some of his drumming played to wider audience ?
Thanks for the drums. As you say, Martin, I will stick with a pattern I know works on Audacity.
I do tend to forget, when moving between computers. It would be nice if there is a pattern. I always use 44KHz as the sample rate, just in case I ever feel like burning a CD. Disk space is not a problem.
So here is a test
Can you see a pattern in that?
Tim's examples above are actually using these sample rates (I determined this by downloading them and opening them up in an editor):
11Khz 16bs okay
16Khz 24bs super chipmunk
22Khz 32bs okay
32Khz 40bs chipmunk
32Khz 48bs chipmunk
44Khz 56bs okay
44Khz 64bs okay
44Khz 80bs okay
44Khz 128bs okay
So when using Audacity to export MP3 for use in Flash (and Moodle), you want to use bitrates where Audacity resamples sounds to 44Khz, 22Khz or 11Khz.
Thank you for your music. Might your music be available for use in listening quizes, under CC's "noncommercial attribution"?
The original Rewd homepage is still available on 'wayback!' Wow... music, poetry, art, and boy-band photos; very interesting.
describes all the posssible sample rate and bit rate combinations for Flash and whether they support mono or stereo. The article is about getting flash to do the commpression, but I think that the sample rates and bit rates that flash can compress to may also be the ones that it supports.
The curse of the chipmunks return.
I have a large file recorded at 44khz. This *should* be okay if I could export to mp3 keeping this sampling rate.
Also, even using Audacity, it should not produce chipmunk audio at 16pbs and 32bps bearing in mind that, as Martin Dougiamas kindly pointed out in his table above, Audacity reduces the sampling rate to 11KHz and 22KHz when exporting to 16bps and 24bps respectively.
However, exporting to mp3 at 16, 24, and 32 bps all seems to produce chipmunks.
and any higher bits per second than that produces a file that is too large. I guess that Audacity is dropping sample rate, as noted above, but in a random way perhaps.
Also, I do not seem to be able to change sampling rate using Audacity, or at least, when I do that in Audacity, the speed of the file slows proportionate to that change so that the file plays e.g. setting the sample rate to 22Khz (from 44Khz) like this,
the file now plays twice as slowly in Audacity. Ignoring this fact and exporting the slow file to mp3 results in
which is still chipmunking (athough it is not far off at "22Khz at 32bps").
Is it time to invest in an audio editor that
1) Exports at the sampling rate that it says it is exporting at
2) Can change sampling rate without changing the speed of the audio
This is a shame. So many of us are using open source Audacity.
In the meantime, as a workaround, it is possible to prevent Moodle from linking resources to the flash player by
1) Turning off this feature globally in the Admin filters settings
2) Using a web page and use the <nolink> tag (i guess)
3) Link as a resource in the same window and check "Put resource in a frame to keep site navigation visible" -- this means that a non flash (non-moodle, in my case windows media player) media player will be used.
The latter is the workaround that I am using now.
What is the name of your band? With that snippet of information, I can trawl the Internet for pictures of you in your heyday, and stick them on parts of this site just when you are least expecting them .
I also use Sorensen Squeeze - another great digital video and audio conversion tool.
Would that be Quicktime Pro, by chance? With QT 7, I don't see many options available for sound conversions.
Thanks in advance.
And, yes, there is a consistent way to get around the problem. If you record your file at one of the rates that Flash supports, it will work fine. If you don't, it won't.
Sorry to say so, Eric, but your post is rather confused (and confusing).
Could you state clearly the different steps you take to get an MP3 file a) to play correctly and b) to play with the chipmunks effect. Could also specify the sampling rate that you use for your MP3 files. Finally, could you say whether the Moodle MP3 Flash player is being displayed or not in either case.
Ok, I made an mp3 file using audacity on my mac. I used 44100hz (as well as 22050 and 11025), default sample format 24 bit, high sinc interpolation, export mp3 setup bit rate of 56. (and another example with the above sample rates but a set up bit rate of 128). I uploaded the files to my moodle site using the standard method so that they appeared in the files section and I could link to them from there.
I also uploaded them to a subdomain of my site using cpanel's file manager.
When I linked to them in the files section of the moodle site, I got the chipmunks.
When I linked to them using the address in the sub domain they were fine.
(the flash player was being displayed normally)
When I created a "link to file or web site" resource and linked to the mp3 in the file section of the moodle site I could hear that fine - but it doesn't show the standard flash player, rather it shows the browser's player.
Now, tonight I redid this process just to make sure that I was right - only thing that happened was they now all worked!
I don't know what the problem was last night - cache??? Tired??? Chipmunks on the roof??? I'm not sure.
It has been a frustrating couple of days! But as it seems to be working now, I'm fine.
Thank you, though, for taking the time to look at the post!