Bits, hertz, bandwidth and mobile audio recording
I find this subject boring but important. So there you have it.
Here are some good links to information on choosing the right sampling rate for audio recordings:
http://audacityteam.org/wiki/index.php?title=Sample_Rates
http://www.cs.cf.ac.uk/Dave/Multimedia/node150.html
http://www.wisegeek.com/what-is-a-good-bitrate-guideline-for-mp3-files.htm
If you’re trying to get those blasted AMR files off your phone and into Audacity, this site can help: http://media-convert.com/
After playing around with various recording levels on my Zoom H2 and Nokia 5300, I can’t see any advantage of saving mp3s at a bit rate higher than 96. I saved a recording at 16, 32, 96 and 128 bits in mp3 format and the 32 bit was acceptable while the 96 was terrific. I could detect no difference between 96 and 128. I think for voice recordings 96 should be a good standard while you can compress audio to 32 for situations where it will be played through FM radio or on inferior sound equipment (read “most of the world”).
Here are the stats on a 32-second recording I made:
| Bit rate | Size | Quality | Application | |
| 16 | 66K | Poor, grainy | Mobile download | |
| 32 | 140K | Slightly grainy | FM Radio | |
| 96 | 419K | Rich sound | mp3 | |
| 128 | 558K | Equal to 96 | CD |
Here are three of the four recordings for your listening pleasure.
The poem is On a Fly Drinking Out of His Cup by William Oldys
Take note that this is for a 32-second recording. A song or a five-minute podcast would be that much larger. I don’t think any of these rates would be small enough to tempt someone to download a file on their mobile. At least here in Africa there are many cheaper ways of getting mp3s through Bluetooth sharing and pirated CDs full of mp3s. In the developed world no one is going to want to download the New Testament on to their phone for example when they can get it faster and cheaper on their computer.
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Hmm… if you save your file as (or convert it to) AMR even in “good” quality it is not quite as good as the 32kbps MP3, but it is streets ahead of the 16kbps version and actually smaller at 55k see here: http://bigbible.org/audio/On a Fly Drinking Out of His Cup 96.amr at “medium” quality it is only 31k and still better than the 16kbps MP3 http://bigbible.org/audio/On a Fly Drinking Out of His Cup medium.amris that size downloadable?
PS, it is of course still sharable by bluetooth etc…
Aagh, the links don’t work because of the space in your filename
so try these:
http://bigbible.org/audio/OnaFlyDrinkingOutofHisCup.amr
http://bigbible.org/audio/OnaFlyDrinkingOutofHisCup-medium.amr
PPS: I converted a 23min 29sec recording that in good (96kbps) MP3 came to over 16MB into acceptable AMR at just 1.20MB is that sort of rate 53K/min one that people might download to share?
Definitely if they were trading via bluetooth or getting it off a computer. I’m on the bleeding edge of mobile Internet usage but I’d never try to download a 1.2MB file.
Just got your messages that got stuck in moderation. Fascinating info on the AMR files. If we’re only looking at a simple voice recording this will work. But once you get into music of any complexity you need a much higher recording sample rate.
If the music is only intros and extros etc. then AMR on high quality on my converter turns a 64K music file from 600K of quite good quality into 119K of tinny tranny quality so if the main focus is on the speech and the mucis is “just” for mood and to introduce etc. then AMR could still work…
96k is indeed generally fine, but one problem with it is that some Flash mp3 player versions stutter and have severe issues with it. This is slowly being dealt with, but it is also still a problem and worth mentioning if your mp3 isn’t just a file floating free on your website.
That’s good to know. Thanks.
What bitrates are safe/safer for such devices?