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anyone good at maths/stuff to do with audio?

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  • anyone good at maths/stuff to do with audio?

    ok so heres the deal im revising for an exam and am stuck on this question

    a)
    Decibels are often used in audio systems to describe signal levels. Calculate the voltages that are represented by the following dBu levels, measured with respect to a reference level of 0.775Volt.
    i) 7dBu
    ii) 0.3dBu
    iii) –70dBu
    (7 marks)

    b)
    The sound recorder program on a PC offers three different digital audio recording formats, shown in table Q2b.

    Format Sample rate Number of bits Mono/stereo
    Voice 11025Hz 8 Mono
    Radio 22050Hz 8 Mono
    CD 44100Hz 16 Stereo
    Table Q2b

    Calculate the bandwidth and dynamic range for each format. Then go on to explain why the chosen parameters are used for each of the different formats.
    now part A i have under my belt, i understand that. but its part B im stuck on, anyone give me some hints on how to work out the bandwidth?
    (i get the dynamic range bit tho)

  • #2
    Re: anyone good at maths/stuff to do with adio

    Audio Bandwidth will be a function of the sampling rate (big hint: nyquist), and dynamic range of the bit depth. The starting hz is 20, but I can't recall why or if that is correct in the context of the question (might be 0HZ).

    Finding data bandwidth IIRC should just be as simple as multiplying of he supplied data to get the bite rate. Just keep your bits and bytes in order when doing the math.

    Spoiler:
    http://en.wikipedia.org/wiki/Streami...th_and_storage


    EDIT: In the context here, I think it is asking for audio bandwidth and why, not data bandwidth. If I were writing the test, I would supply both datasets.

    Comment


    • #3
      Re: anyone good at maths/stuff to do with adio

      cheers 4glory, but i think thats the wrong type of bandwdth, after searching i found this definition of audio bandwidth


      AUDIO BANDWIDTH
      The range of audio frequencies which directly influence the fidelity of a sound. The higher the audio bandwidth, the better the sound fidelity. The highest practical frequency which the human ear can normally hear is 20 kHz. An audio amplifier which processes all frequencies equally (flat response from 20 Hz to 20 kHz) and a reasonably high signal-to-noise ratio, will faithfully reproduce the full range of perceptible sound.

      so, now im just Über confused!

      my mates think it could simple be as simple as the sample rate - 20 as 20hz is the lowest freq the human ear can hear... then again it might not

      Comment


      • #4
        Re: anyone good at maths/stuff to do with adio

        Spoiler alert:


        Format Sample rate Number of bits Mono/stereo
        Voice 11025Hz 8 Mono
        Radio 22050Hz 8 Mono
        CD 44100Hz 16 Stereo

        Calculate the bandwidth and dynamic range for each format. Then go on to explain why the chosen parameters are used for each of the different formats.
        Due to the way waveforms are digitized, the highest hz you can sample will be half the sampling rate, above this hz you will get audible artifacts becuase the waveform will be smaller than the resolution of the recording points. (Nyquist theory) A brick-wall filter (48db or 96db/octave iirc) prevents these artifacts from being made.

        Thus, a sampling rate of 11025hz will record up to 5512hz. this is sutabile for speech as the human speaking voice doesnt produce much above this. Radio will do up to 11025hz (the large chunk of the audible spectrum), and cd will do 22050hz covering (theoretically) the range of human perception.

        :)

        I hope I'm helping, I paid $30k for a piece of paper about this crap that I already learned in a $20 text i bought used. (master handbook of acoustics 6th ed) Might as well fell good about the waste of my college years.

        Comment


        • #5
          Re: anyone good at maths/stuff to do with adio

          cheers again 4glory :) that has somewhat made it easier

          so im guessing the bandwidth is 5512?

          Comment


          • #6
            Re: anyone good at maths/stuff to do with adio

            n-5512, It should be expressed as a "range". But a "bandwidth of 5512hz" probably would be a good answer in this context.

            And be aware there is a decimal place in there, do the math incase I made a typo. I can't recall if there was a standard 20hz starting point for digitizing or if it simply took it from DC.

            Don't forget stereo is twice the data and there is a reason the other two are only mono.

            Comment


            • #7
              Re: anyone good at maths/stuff to do with adio

              The question is ambiguous: What kind of bandwidth is wanted?

              http://en.wikipedia.org/wiki/Bandwid..._processing%29

              The digital bandwidth (or bit rate), measured in bits per second, is simply the sampling rate times the bits per sample:

              bits/second = samples/second * bits/sample

              Hz is sometimes used as a shorthand synonym for samples/second, but one should use the latter for precision.

              Baseband audio bandwidth is half the digital sampling rate.
              Dude, seriously, WHAT handkerchief?

              snooggums' density principal: "The more dense a population, the more dense a population."

              Iliana: "You're a great friend but if we're ever chased by zombies I'm tripping you."

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              • #8
                Re: anyone good at maths/stuff to do with audio?

                its ok, a question on this didnt turn up :) so im happy now! all my exams are over!

                cheers for the help tho guys

                Comment


                • #9
                  Re: anyone good at maths/stuff to do with audio?

                  Originally posted by browna3 View Post
                  all my exams are over!
                  Congrats, now go enjoy life!
                  |TG-Irr| westyfield

                  Sig pic by Sonic, avatar by Chalcas. Thanks!
                  Irregular since 2007.

                  Comment

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