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Thread: Query

  1. #1
    New Lounger
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    Query

    Query: Does 96K bits per second equal 44K Hertz???

    Or doesn't this question make any sense???

    Thanks.

  2. #2
    ileacy
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    Re: Query

    Sort Of.

    Digital sampling of audio requires at least 2 bits per cycle.

    22KHz Stereo (2x22Khz=44KHz) requires a minimum of 88Kbps. Depending on the encoding, additional bits may be added to the stream for error detection/correction.

    Real requirements vary with the type of audio. Eg. Spoken word is fine at FM quality (64Kb), Old AM mono music (eg. 50's R&[img]/forums/images/smilies/cool.gif[/img] is usally fine at 96Kb, but classical, jazz, or anything else with lots of dynamic range needs 160 (ie. oversampled). 320Kb is overkill.

  3. #3
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    Re: Query

    Additionally, a Byte = 8 bits, maybe more if parity is checked.

  4. #4
    Uranium Lounger
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    Re: Query

    Something else that makes a big difference is the software used to encode audio. MP3 does not approach CD quality until you hit 128 Kbps, whereas Microsoft's WMA format can use a lower bitrate.

    Most of this is determined by your ability to hear the audible artifacts in the encoded sound, and the amount of space you are willing to sacrifice. For example, using the ever popular MP3 format, 128 is the popular bitrate - but some encoders don't do a good job even there. Higher bitrates (160, 190, 256) sound better but consume a noticeably larger amount of disk space.

    Remember, when you encode audio onto a computer, you are "tossing out" some of the original music - much as JPG image discards color information from pictures.
    -Mark

  5. #5
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    Re: Query

    Does to 64Kb apply to Voice-Over-IP, or is that a whole different matter. Just curious, so don't worry if you don't have a ready answer.
    Granville

  6. #6
    ileacy
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    Re: Query

    You can set VOIP quality but the default is 8kbps of compressed audio.

    For comparison, the original telephone networks of the 80's used 4.5khz of uncompressed analog in the normal spoken voice frequency range for transmission. This translates to 9kbs of raw digital.

    The 64kbps WMA format that I use for spoken word audio is used for Audio Book and Comedy CD's. It is more than needed but I prefer to err on the side of quality.

    I also have a collection of old radio shows. They are in 32kbps MP3. Play fine, but, I don't have originals to compare them to.

  7. #7
    Uranium Lounger
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    Re: Query

    It's also worth noting that voice is vastly different from music when it come to encoding it. To accurately reproduce voice, far less bandwidth is needed, simply because the range of human voices is limited. In music you have a dynamic range from about 20-40Hz (more felt than heard) to 16KHz (and beyond on hi end stereos).

    Telephones are filtered below 400Hz and above 3,400Hz. An interesting example can be found at <A target="_blank" HREF=http://www.howstuffworks.com/telephone3.htm>How Stuff Works</A>.

    So, cutting to the chase, it requires less data to reproduce voice and thus the encoding rate can be lower. Ian, I'd bet dollars to donuts that the same applies to the older radio shows that you have, since hi-tech recording sprung up in the mid 1960's (subject to debate of course).
    -Mark

  8. #8
    ileacy
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    Re: Query

    You are correct. The 4.5KHz is the frequency division multiplex spacing for telephone. Usable bandwidth is as you stated.

  9. #9
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    Re: Query

    Ian and Mark, thanks for your replies. I think I understand a little better now.
    Granville

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