Audio Sample Rate Changes After Publishing
Jun 08, 2016
Hi Storyline community,
I'm having a quality issue with the audio that is published from Storyline, which I'm fairly sure is due to Storyline changing the sample rate of the audio to 22050 Hz while publishing. I've searched the community, but have only found discussions related to the audio bit rate in the Publish Quality settings, which is something different altogether.
This seems to happen regardless of audio format input into Storyline (mp3, wav, etc), as well as the sample rate and bit rate of the input audio. Changing the bit rate in the publishing settings does not seem to affect the sample rate either.
My question is this: Is there any way I can change how Storyline handles the sample rate on publishing?
One solution: I can replace the published audio files with the pre-Storyline original audio, but this is not practical for projects with lots of audio, especially because Storyline randomizes all of the published filenames. I'm hoping there is a better way to do this. Maybe this needs to be a feature request.
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For those interested, here are some technical details about the issue, and an explanation of why this is a problem.
Technical Details
It appears that the audio files are changed to a sample rate of 22050 Hz upon publishing, which is exactly half of the CD-quality standard of 44100 Hz. This is a big deal, because it truncates much of the high frequencies in the audio. Without going into details about Nyquist's Theorem, a sample rate of 22050 Hz implies that all frequencies above 11025 Hz are cut off.
By cutting the higher frequencies, the audio loses a lot of the "air" and "brilliance" on professionally recorded voiceovers. It's even worse for music, which tends to use the full spectrum of human hearing (roughly 20Hz to 20kHz).
I've added the following attachments to show the results:
- Before_Storyline.mp3 (This is the source audio before being added to Storyline - 128kbps 44100 kHz)
- After_Storyline.mp3 (This is the audio published by Storyline using 128kbps publishing quality - 128kbps 22050 Hz)
- Before_and_After.png (This shows the difference between the two audio clips on a spectogram. Note how the second clip is chopped off around 11kHz.)
4 Replies
Hey, Matt.
Thanks for the thorough explanation of your findings. What we try to do is publish audio that balances the highest possible quality with the lowest possible file size. Right now, you won't be able to change the sampling rate, but the method you mentioned (manually replacing the audio files in the published output) is an effective workaround, and as you suggested, we always welcome Feature Requests!
Good luck with your project!
Hi Ashley,
Thanks for the reply.
The strangest thing about this is that not only is 22050 Hz a non-standard sample rate, but there is no actual difference in file size in using that sample rate for mp3 files.
Since the mp3 format uses a specific bit rate (128kbps in my example) it is locked in at a certain amount of file size per second of audio. Even though the sample rate is lower, the file size is the same. In fact, in the two examples I sent, the post-publish audio is actually slightly larger than the pre-publish source audio.
Changing the bit rate in the publishing settings makes sense, because that is a good way to affect file size, but I think the sample rate should be set to an industry standard, such as 44100 Hz or 48000 Hz.
I'll put in a feature request about this.
Thanks again!
Thanks Matt for putting in the feature request - and hope you have a great weekend!
Hi Matt!
We've heard you loud and clear! Today, we released Update 33 (Build 3.33.20625.0) for Storyline 360.
You'll find that one of the fixes in the update includes the option to turn off compression for audio files!
Now all you need to do is update Storyline 360 in your Desktop App! You can see all the new features and bug fixes in the updated Storyline 360 Version History!
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