AUDIO QUALITY

Discussion in 'General Electronics Chat' started by n9xv, May 3, 2005.

  1. n9xv

    Thread Starter Senior Member

    Jan 18, 2005
    329
    1
    Hi, just a question about audio CDs. What are the technical specifications implied when you hear the term CD quality. Most of the files on my MP3 player are at a bit rate of 128-kbs. Most streaming audio stuff like napster is 192-kbs. If I rip tracks from a CD and and convert them to MP3 files am I sacrificing audio quality. Can I really discern a difference between typical 128-kbs .WMA files on my MP3 player or CD player as opposed to 300-kbs or .WAV files.

    Thanks
     
  2. n9xv

    Thread Starter Senior Member

    Jan 18, 2005
    329
    1
    No takers on this one? C'mon, you guys are holding out on me.
     
  3. n9xv

    Thread Starter Senior Member

    Jan 18, 2005
    329
    1
    No takers on this one? C'mon, you guys are holding out on me.
     
  4. n9xv

    Thread Starter Senior Member

    Jan 18, 2005
    329
    1
    Have no idea why that posted twice?
     
  5. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    CD quality is 44.1Khz Sampling with 16 bit precision, which is 705kbs.

    Typically, the human is a band pass filter with our center frequency about 1-3Khz. We hear high frequency and low frequency no where near as well. As a result, MP3s became popular because what you loose when you do audio compression is the higher frequencies. Typically, MP3s stick to 16 bit sound but they sacrifice sampling speed. A 300 kbs signal is only smaples at 18.75Khz. About 1/2 the possibly quality for a CD. Now, with the Nyquist sampling criteria, you need to samples more than 2x the highest frequency you intend to keep. For CD, since our ear can hear up to 20Khz, they samples at 44.1Khz. At 18.75 Khz, the best frequency you wuill hear will be about 9Khz. Since all human speach, most guitar riffs, all drums save the cymbols and just about any sound we make resides well below 9Khz we barely notice a difference, but if you listen closely, you will notice the difference in the cymbols first as a kind of wooshing or changing wind sound inthe back ground. This wind sound is called aliasing whereas a high pitched sound will now sound like a lower pitches sound since the sampling frequency can not handle the high frequency any longer.

    Typically, if you use a head set, or standard stero with analog speakers and analog signal you will most likely not hear any of the wind since the lack of quality of your speakers will over take the noise added by aliasing.

    I have a set of Digital speakers i have connect to my PC since I used to havea little at home studio and I can always hear a difference between an MP3 and a .wav. Part of this is no noise in the signal since its digital as well as the higher level of encoding my digital system generates. Rather than the typical 44.1 khz CD setup, its generates at 48,000 which is 768kbs, or higher than CD quality. As a result, I can hear massive differences between MP3s and CD music, but we'retalking spending stupid money to hear the difference.

    If you encode in the 256kbs+ range and intend to use in your car, mp3 players, headset, you'll be fine. They will take a little more room than the typical 128 and 192kbs encoded MP3s, but you will have better quality of sound.
     
  6. ouabache

    Member

    Jul 12, 2005
    11
    0
    Kevin,
    I enjoy working with audio files and ripped quite a few through the years. I do concur with Brandon's discussion. He makes some excellent technical points.

    My two cents are more qualitative. The attraction of mp3s for me is their small size while maintaining an acceptable level of quality. My ear is pretty good, I'm a musician and born with perfect pitch (a trait that is common in my family). I have tried many sampling rates and found that 128kbs sound great!! For the difference in time to edit and relative size, I cannot justify saving at larger sampling rates. As far as telling a difference between files sampled at 128kbs or greater; if I was just listening, I would be hard pressed to tell the difference.
     
  7. Hood

    New Member

    Jul 10, 2005
    3
    0
    I am an audiophile, and have a CD collection of over 1000 albums.. I record everything to MP3 at 320 and love the portability of my MP3 player. With that said it is nowhere near the quality of a CD, and anyone that tries can hear the difference if the equipment isn't the limiting factor. I won't even listen to music purchased off the net at 128, sounds terrible.

    When doing a test on this, I recorded the same song at 128, 196, 320 and wav which my MP3 player can play.. I did alot of AB testing and everyone that tried could tell the difference in quality everytime I stepped it up.. I tried tricking people and even people that didn't have well trained ears could tell me which was the higher fidelity version.. I was suprised that everyone could tell the difference between the 320 and WAV files..

    I then put all of the MP3 files onto my brother's IPod, and people could only tell the difference on the 128 and 196 files, after that it was a guessing game.. I couldn't believe how much better my Creative MP3 player sounded over the IPod.. It really depends on the environment and the equipment as to if you can tell the difference. If you run good equipment the file sizes are critical, if not you will have to do a similiar test yourself to see if it makes a difference in your environment and to your ears..

    Goodluck,

    I recommend the CDex program to rip your MP3s using the Lame encoder.. Best I have tried..
     
  8. ouabache

    Member

    Jul 12, 2005
    11
    0
    Since my comments were qualitative, I should have realized I would be opening a can of worms. I understand everyone will have an excellent opinion on what sounds good to them. However, even music CDs admit a loss in fidelity. It has been noticed that audio quality diminished with the switch from LP (analog) audio to CD. An excellent discussion on the shortcomings of CD audio format may be read at this reference.

    They point out (as did Brandon), present CD format uses 44.1KHz sampling frequency, but go on to say that fidelity above 20KHz is limited by artifacts of digital noise. CDs also use 16bit resolution which translates to 65,536 voltage steps. This resolution has been noted to introduce a graininess to CD audio quality.

    However DVDs overcome this limitation. Each has the capacity to hold 3 1/3 times more data than a standard CD. Music may be sampled at 96KHz with 24 bit resolution and accomodate a full CD worth of music. An analogy is that for each voltage step that a CD resolves, a DVD can subdivide into 256 additional steps.
    So maybe we should start thinking about updating our audio collection to DVD-audio . <grin>
     
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