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Topic: Tips on retaining quality when converting audio files

  1. #1

    Tips on retaining quality when converting audio files

    Does anyone have any tips on retaining as much quality as possible when converting an audio file to a lower bit rate/sample rate? So if for example I converted a 44k/16 bit file down to 8bit/22k or 11k. Also are there any audio conversion programs that are particularly good at retaining that quality at lower rates or is it just a matter of the technique you use to do it?

    I hear a lot of low quality files that sound quite good considering. Whenever I do a conversion to a low rate everything turns completely awful... [img]images/icons/frown.gif[/img]

    King, perhaps you know a lot about this? [img]images/icons/smile.gif[/img]

    Thanks in advance.

  2. #2

    Re: Tips on retaining quality when converting audio files

    Hi Hasen,

    Assuming you already know this: dithering is essential when you convert from a higher bit-rate to something lower. Try and use POWr-dither when you convert. If you \'forget\' to dither you get an huge increase in quantization noise - which is most likely the case when you speak of awful results. Also use a low-pass filter before you start converting; you don\'t need the highs anyway when you\'re going down to 12 bit @ 22.1kHz. And, last but not least, remember to make as much use of the bit-range. Audio which doesn\'t (not normalized, compressed or maximized enough) will have more quantization noise.

    A good program for all this is AudioEase Barbabatch (Audio Ease) . It\'s been around for some years already but it\'s still the best conversion program I know of. It converts bit-by-bit and is way better than some other utilities out there.

    Hope this info is useful! [img]images/icons/smile.gif[/img]



  3. #3

    Re: Tips on retaining quality when converting audio files

    It also depends on what you mix down. There is much about the choice of instruments (that what makes other mixes sound \'good\' at 22k). I wouldn\'t expect a full orchestra can do an impact at 22k. From what I heard you can achieve better results making an almost completely electronical track (with \"synthy\" sounds). You should avoid instruments that need the full range as much as instruments that need too much of either end (too low or too high). You can also improve the mix with EQing taking lows and highs a bit out.

    I\'m assuming you do this for saving space (bandwidth issues in the internet). You should also consider if it\'s enough to provide mono instead of stereo (which is IMO at 11k nonsense). Or for internet issues look at streaming formats but that is a completely different question.

    Hope this helps! [img]images/icons/wink.gif[/img]


    PS: As you were one of those, remember how trackers got around these points, examples: Purple Motion...

  4. #4

    Re: Tips on retaining quality when converting audio files

    Its all been said [img]images/icons/smile.gif[/img]

    It all really depends on the end usage [img]images/icons/smile.gif[/img]

    filtering before hand definitely helps bad conversion algorithms. And converting from 44.1 to 22.050 creates less \"errors\" and aliasing since the mathematics are simpler.

  5. #5

    Re: Tips on retaining quality when converting audio files

    Thanks everyone, out of all these suggestions I\'m finding that the most important thing is the source. Coming from a 24bit source seems to yield much better results than 16bit. It seems obvious but I didn\'t realise it would be that substantial a difference.

    Hansi, yes I was a tracker but I never really cared much for keeping my mods small - I was always using the best quality samples I could and ended up with ridiculously large mods. I outputted into mp3 so it didn\'t matter really. So you can see that I haven\'t much experience with maintaining quality with sample conversion. [img]images/icons/smile.gif[/img]

  6. #6

    Re: Tips on retaining quality when converting audio files

    you may also want to EQ for definition.

    Usually high quality stuff cuts and \"sparkles\" way higher than what you\'d get in some lower bit rates like 11k, so you need to re EQ to make it sound better in the limited frequency range you have.

    like removing some low mids to clean up \"mud\" thats normally \"meat\" to out other mixes [img]images/icons/smile.gif[/img]

  7. #7

    Re: Tips on retaining quality when converting audio files

    Try using an \'exciter\' plug-in, preferably after conversion with dither. I have found Sound Forge dithering to work reasonably well. You might try the \"Spectralizer\" plug from Steinberg as avery good exciter. I don\'t know for sure if it works on all sample rates/bit depths, but it IS the best exciter out there! Btw, the suggestion on pre-filtering is good advice, and the exciter can restore whats lost...somewhat.

  8. #8

    Re: Tips on retaining quality when converting audio files

    8 bit will always sound like poo, you only have 256 levels of amplitude if the source file is normalized to 0db. And the lowest frequencies act as a carrier for the higher frequencies, which we are much more sensitive to, so you\'ll get much less resolution for higher frequencies.

    Also you need to \'brick wall\' filter at 1/2 the sample rate, frequencies above that will spray back and become represented as lower frequencies. Is that clear? 22K sampling can\'t represent tones above 11K (it will even muck up frequencies near 11K depending on the phase where these tones get sampled)

    What are you trying to do, mimic the sound of RealAudio or dump your work to a Speak \'n Spell or somesuch?

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