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    Audio editing

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    WhiteBoy
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    Audio editing

    Post  WhiteBoy on October 10th 2011, 10:37 am

    Good or bad idea?
    Do you want to reduce file size? Good idea.
    Do you want to preserve quality? Bad idea.

    I should have correctly typed "signal-to-noise ratio" instead of "noise-to-gain ratio" (holdover from my college radio days, sorry).

    Without devolving into horribly detailed math, you can think of each audio track as a speaker.
    Each speaker contains signal (desirable audio) and noise (undesirable audio).
    Let's assume a low signal-to-noise ratio, by valuing signal as "3" and noise as "2".
    With one speaker, we get three parts signal for every two parts noise (3:2), for a total volume of "5".
    With two speakers, we *multiply* the values, getting a signal-to-noise ratio of 9:4, more than twice as much desirable audio as undesirable audio, and a total volume of "13".

    Most microphone/recording systems used at home have a fairly low signal-to-noise ratio. You can find this rating on your packaging in most cases. A typical rating is 70dB, or a 94dB:24dB ratio. A good professional microphone will have a rating between 200dB-400dB, or even better.

    But this is just the math. Probably you should rely on the difference detectable by your ear...

    Thanks for getting into the more "techie" side of things a little bit, Mindspike. How does adding a second speaker multiply the signal by 3 but the noise only by 2? That sounds more like it was squared instead of multiplied.

    I've been dabbling a little bit in sound editing because I've recently been turning our church's sermons into a podcast. I could not tell a difference in the audio quality of mono vs. stereo. We have (I'm sure) a low-quality microphone because (I'm sure) it is one of those wireless mics that a small/med-size church can afford to buy. With a higher quality source, maybe the difference would be discernible?

    Currently I cut the audio how I want it and then send it through a "script" (can't think of the term Audacity uses for macros right off) to clean it up. The "script" does the following things, not necessarily in this order: normalizes, changes it to mono, cleans up clicks, cleans up silent spaces, at the end normalizes again while increasing the gain, and maybe another thing or two (sorry, I'm not at home so don't have it in front of me). Would it be better to change it to mono at the end or beginning of the script? From your description it sounds like I am possibly missing out on some audio quality that the script may be able to enhance before I strip it out and make it mono.

    Thanks for any tips you can offer to an audio noob.

    WhiteBoy


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    mindspike
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    Re: Audio editing

    Post  mindspike on October 10th 2011, 4:24 pm

    Actually, both values are squared. Add a third "speaker" and the values would be cubed. Real audio doesn't work exactly this way, but it's a pretty good approximation.

    With a fairly low dB rating, it's even more important to preserve audio information, especially during the scripting process. My advice? I believe you will obtain better results by applying your Audacity script to the raw data and crushing to mono after you're done.

    With a sermon-type product, where you're essentially only dealing with a single voice, you've got a lot of leeway to manipulate the audio without losing quality, but unfortunately, not a lot of quality to be gained by extensive manipulation of the data.

    Sounds to me like you've got the basics in the bag. A touch of noise reduction might contribute, as would a 2-5% boost in bass and reverb. But honestly, if it sounds good to you, I'd run with it. Your final bit rate encoding has quite a lot to do with the quality of the audio, and there is only so much to be squeezed out of 64kbps, a common value used for podcasting sermons.


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    WhiteBoy
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    Re: Audio editing

    Post  WhiteBoy on October 10th 2011, 5:56 pm

    OK, that makes sense. I'll adjust my script to make it mono at the end. Thanks for the tip!

    The script does some noise reduction, but I don't think it does any bass or reverb. I will check and play with it if not. I have recently been boosting the gain a bit to get a little more volume.

    The quality sounds acceptable to me, but I also think there's room for improvement. When I encode them, I do it as VBR level 5 which works out to about 64-75kbps. I toyed with it in the 32k range but those didn't sound good enough to me. And I couldn't really tell much improvement in going higher than level 5.

    wb


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    Re: Audio editing

    Post  Paeter on October 10th 2011, 6:48 pm

    y'all are smart.


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    mindspike
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    Re: Audio editing

    Post  mindspike on October 11th 2011, 3:56 pm

    shucks, I jest taked some math 'n radidio classes in colluj
    lotsa this'n stuff's the same


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    WhiteBoy
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    Re: Audio editing

    Post  WhiteBoy on October 11th 2011, 7:46 pm

    lol


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