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Microsoft's OneNote supplied with Office2010 does very well for note taking software. It includes the function to record audio/video, or just audio. The options in the program for Codec are a) Windows media audio 9, b) windows media audio 9.2, and c) windows media audio 10 professional. Especially in the case of the latter Codec, many formats are available, from <0kbps, 8kHz, mono CBR>, to <320 kbps, 44kHz, stereo (A/V> CBR>. They seem to be divided into two categories: (A/V) and non-A/V (whatever that means, I don't know), and then according to their kHz, and then from kbps. Thrown in also are options for stereo, mono, and what's called "low delay CBR".

With a basic understanding of these terms, one could likely guess that 320kbps 48Khz CBR is overkill for this philosophy of use, and 0kbps 9 khz, mono CBR leaves something to be desired in quality, especially with 1tb hard drives around these days. However, answering the question of precisely which format would be most well suited to this philosophy of use is another question that might require a different level of knowledge than most people would have. One could take the try-it-and-see approach, but this question seems to well suited to superuser to pass up the opportunity to post.

So, my question is: Which Codec/Format combination would be most well suited to the philosophy of use of recording audio for notes, in a large or small lecture hall. That might be two questions; would a certain codec be desirable in certain sized rooms?

p.s. subquestion: What does, in the windows media audio 10 professional codec, the format (A/V) designate?

eichoa3I
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1 Answers1

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  • Bit rate is how well the audio can be approximated by a given amount of data. Too low bitrates introduce garbled voice, strange artifacts and unnatural, smoothed out transients (short sounds like the letter T). Higher bitrates will match the original content more closely, but potentially uselessly if the benefits are not clearly audible (overkill). Variable bitrate will always provide better quality that constant bit rate CBR at the same given bitrate, since the encoder than concentrate more effort (data) on the hardest-to-encode parts.

Let's call bit rate: Audio integrity.

  • Sample rate affects the possible frequency spectrum an audio file can have. The Typical value is 44khz, since it practically covers the entire audible range (0-22khz). By reducing the sample rate you are dropping higher frequencies which won't be encoded anymore, making it easier to encode what's left with better integrity. However, reducing the sample rates may alter background noise which is present in most recordings, and that may provided undesired side-effets (sharper noise), and eventually sibilance issues ("s" sounds) or plain lifelessness - even at very high bitrates. Lowering the sample rate can be a very effective trade-off when working in very low bitrates; Voice over IP telephony protocols are an excellent demonstration of that.

Let's call sample rate Audio richness.

  • Stereo: if your sound is mostly mono, like speech, you are wasting half the bandwidth by encoding it as stereo (unless it is joint stereo, but that's another story).

With music, I think it's that it's common knowledge that 128kbps 44.1khz stereo with MP3 is the tipping point where some music degradation is perceptible to almost anyone, while still being listenable. Since speech is easier to encode than music, I think its mono equivalent -MP3 64kbps 44.1khz- provides a great starting point with ample quality for most purposes while not being overkill.

Finally, Windows Media Audio is intended to be much more efficient than MP3. So you could easily offset these reference points by 25-40% (eg. WMA 40kbps should be similar to MP3 64kbps). WMA Professionnal is intended to be better than WMA 9, apparently reducing the number of low-bitrate encoding options that WMA9 has and automatically use the best method for most content. So unless you need to play it back on devices that only supports WMA9, it's likely the better option.

Hopefully you can work your way up (or down) from there.

mtone
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