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Thread: Audio advisor suggests using PC as head unit is horrible...

  1. #21
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    Quote Originally Posted by WuNgUn View Post
    You do realize, that the S/PDIF digital audio format COMPRESSES the signal?
    Even the TOSLINK optical interface uses compressed data.
    Some of the earlier TOSLINK equipment (not PC's) used raw PCM audio data, but almost everyone now follows the IEC 61937 S/PDIF compression format...

    With that said, a pure digital signal thru TOSLINK would be an option in the noisey car...the TOSLINK won't pick up any EMI at all.
    This isn't true. SPDIF (coax or optical) can permit compressed data, such as audio from a DVD for instance, but not necessarily. The SPDIF format pre-dated the introduction of multi-channel formats, and was essentially used for high-quality 2-channel audio. For example, the SPDIF output of a CD transport is NOT compressed.
    See http://www.tech-faq.com/spdif.shtml
    As far as I know, the standard SPDIF output of a PC sound card is NOT compressed, and is almost universally compatible with any old DAC designed to accept SPDIF. There are threads on how to achieve "bit perfect" outputs from your PC all over the internet, if you're interested.

    To the OP, your audio advisor was partially correct. If you hook up the analog output of most standard sound cards (or worse, the one built into your motherboard), you're getting a lousy signal. The SNR of a cheapo sound card is typically pretty bad (60-80dB), and the frequency response is not flat from 20Hz to 20kHz. If you're not planning on upgrading your sound card, you will likely be disappointed with the sound quality.

    My suggestion would be to get an upgraded audiophile-grade sound card (will likely cost $80-$150), which will give you a low-noise analog out. If your car amp or processor has digital-in, even better - you can use the digital output on your sound card.

    SG

  2. #22
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    I think, from my understanding, if your transmitting 2 channel audio thru the digital out, it CAN be uncompressed. Anything more than 2 channels, and it HAS to be compressed...
    I guess if your DAC can't decode compressed data, then you'd know for sure!

    As far as CD transports, which are 2 channel, and the fact that you have to at least pre-amp the signal from a CD player, why would it be compressed from the CD player anyhow? Which doesn't really matter in this discussion...

    To the best of my knowledge, you can transmit 2 channel uncompressed digitally thru optical, and at high bit-rates, but basically any more data than that, it doesn't 'fit down the pipe' without compressing it...
    Whether or not the soundcard WILL transmit uncompressed in 2 channel (I'm thinking it would be just easier/cheaper to design a card to send everything thru the compression stage before outputing), is something the OP needs to research (good luck!) if he's interested...

    From your link;
    "The S/PDIF interface is used to transfer compressed digital audio (as defined by the IEC 61937 standard), and carry the signal between the output of a computer or DVD player to a home theater system designed for Dolby Digital (or DTS surround sound)"
    But we're basically using the sound card as a pre amp...if you used an optical CD drive in your car (I doubt it), then you could connect it optically, without compression to the soundcard (if it supports S/PDIF optical IN. I have RCA S/PDIF IN on my cards, but then your suseptible to noise again)...
    On the digital output stage of the soundcard, I can almost guarantee it's going to get compressed...

  3. #23
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    Quote Originally Posted by WuNgUn View Post
    I think, from my understanding, if your transmitting 2 channel audio thru the digital out, it CAN be uncompressed. Anything more than 2 channels, and it HAS to be compressed...
    I guess if your DAC can't decode compressed data, then you'd know for sure!
    This is correct. The digital output when playing things like mp3's, windows sounds, etc. is UNcompressed.

    To the best of my knowledge, you can transmit 2 channel uncompressed digitally thru optical, and at high bit-rates, but basically any more data than that, it doesn't 'fit down the pipe' without compressing it...
    This is also correct. SPDIF can transmit multichannel compressed digital data like DTS, DD, etc. If you're playing back a DVD/BD you can choose to output the native compressed multichannel sound through your SPDIF. However, this is the native output of DVD's and BD's anyway! There is no loss in sound quality by using SPDIF.

    Whether or not the soundcard WILL transmit uncompressed in 2 channel (I'm thinking it would be just easier/cheaper to design a card to send everything thru the compression stage before outputing), is something the OP needs to research (good luck!) if he's interested...
    It will. All soundcards I've ever seen are capable of outputting uncompressed 2-channel audio. That's the basic standard format of SPDIF. HOWEVER, only SOME sound cards are capable of outputting the compressed multi-channel formats natively. Furthermore, only SOME external DAC's are capable of decoding such a multichannel signal, vs. all are able to convert a standard 2-channel uncompressed signal.

    From your link;
    "The S/PDIF interface is used to transfer compressed digital audio (as defined by the IEC 61937 standard), and carry the signal between the output of a computer or DVD player to a home theater system designed for Dolby Digital (or DTS surround sound)"
    Read the part about the Channel Status Bit.

    SG

  4. #24
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    Quote Originally Posted by _Dejan_ View Post
    I have one question.
    My Commell LS-373 have Realtek ALC888 onboard sound card. If someone compare this Realtek ALC888 Sound card with some other USB card? I will use digital out(optical) connected to processor(Audison BIT ONE)... So is in optical out any diference?
    You have to make sure your sound card doesn't resample native 44.1kHz to 48kHz and back to 44.1kHz. Many cards, especially the ones that support AC97, do this. If your card doesn't internally resample, then you still have to bypass windows kmixer because resampling can also occur there too. There should be a thread on "bitperfect" on this site - definitely check it out. If you satisfy all the requirements, and your card supports it, you will be able to get a pure, unaltered, 44.1kHz 16-bit signal at your digital output.

    SG

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    Woo, lots of technical discussion since I last posted. I took a look at the white paper rijndael suggested. There is a lot of useful information in there regarding PC optimization, I don't think I'll be converting all my CDs to 24-bit 44.1kHz WAVs though.

    So, walk me through this thought process. I know some of the responses here have been in regards to Dejan's question, so I might be intermingling things. Right now I use my iPhone with my stock aux jack. Basically I have my iPhone docked in a charger/player which uses the dock connector. This has a 3.5mm cable which I have plugged into a ground loop isolator, which then goes into my car's aux jack.

    If I'm not mistaken, the signal from the iPhone (or at least the dock/charger) is line level. The ground loop iso gets rid of my engine whine and other interference. My aux jack is then connected to my head unit which amplifies the signal to the car speakers. To me, this sounds very good in my car. There's no interference (as a side note I was extremely surprised how well the ground loop iso worked) and the quality sounds fine to me.

    My question is, what is the difference between this and going from the line out on a PC to an amp to the speakers? Isn't it an identical path?

    On a question related to other posts in this thread, I assume SNR is signal to noise ratio? This link: http://www.cnet.com.au/mp3players/mp...62302-2,00.htm indicates the iPhone has a SNR of 83, some forum posts (http://forums.ilounge.com/archive/index.php/t-3902.html) suggest it is over 90, up to 95. http://download.intel.com/support/mo...45013002us.pdf says the SNR of the D945GCLF2 board is at least 90. So, while conventional thinking would insinuate that PC audio is worse than an iPod/iPhone, doesn't these numbers indicate they are similar, or is this just one piece of the puzzle?

  6. #26
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    Hi guys,
    About my onboard sound card which use Realtek ALC888...
    Few informations about ALC 888 you can find HERE
    and if I copy few data:
    Code:
    Hardware Features
    # Hardware Features High-performance DACs with 97dB SNR (A-Weighting), ADCs with 90dB SNR (A- Weighting)
    # Meets performance requirements for Microsoft WLP 3.0 Premium desktop and mobile PCs
    # Ten DAC channels support 16/20/24-bit PCM format for 7.1 sound playback, plus 2 channels of independent stereo sound output (multiple streaming) through the front panel output
    # Two stereo ADCs support 16/20/24-bit PCM format, one for stereo microphone, one for legacy mixer recording
    # All DACs supports 44.1k/48k/96k/192kHz sample rate
    # All ADCs support 44.1k/48k/96k sample rate
    # 16/20/24-bit S/PDIF-OUT supports 44.1k/48k/96k/192kHz sample rate
    # 16/20/24-bit S/PDIF-IN supports 44.1k/48k/96k/192kHz sample rate
    # Up to four channels of microphone array input are supported for AEC/BF application
    # High-quality analog differential CD input
    # Supports external PCBEEP input and built-in digital BEEP generator
    # Software selectable 2.5V/3.75V VREFOUT
    # Two jack detection pins each designed to detect up to 4 jacks
    # Supports legacy analog mixer architecture
    # Wide range (–80dB ~ +42dB) volume control with 1.5dB resolution of analog to analog mixer gain
    # Software selectable boost gain (+10/+20/+30dB) for analog microphone input
    # All analog jacks are stereo input and output re-tasking for analog plug & play
    # Built-in headphone amplifiers for each re-tasking jack
    # Two GPIOs (General Purpose Input and Output) for customized applications
    # Supports anti-pop mode when analog power AVDD is on and digital power is off
    # Supports digital microphone interface for improved voice quality 48-pin LQFP ‘Green’ package
    
    Software Features
    # Meets Microsoft WHQL/WLP 3.0 audio requirements
    # WaveRT-based audio function driver for Windows Vista
    # EAX™ 1.0 & 2.0 compatible
    # Direct Sound 3D™ compatible
    # A3D™ compatible
    # I3DL2 compatible
    # HRTF 3D Positional Audio
    # Emulation of 26 sound environments to enhance gaming experience
    # 10-Band Software Equalizer
    # Voice Cancellation and Key Shifting in Karaoke mode
    # Realtek Media Player
    # Enhanced Configuration Panel to improve user experience
    # Microphone Acoustic Echo Cancellation (AEC), Noise Suppression (NS), and Beam Forming (BF) technology for voice application
    # ALC888DD-GR features Dolby® Digital Live and DTS® CONNECT™ software (Optional)
    # ALC888H-GR features Dolby® Home Theater(software feature)
    What do you think now? Is good enought? I will use optical out.

  7. #27
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    Quote Originally Posted by stratosigma View Post
    On a question related to other posts in this thread, I assume SNR is signal to noise ratio? This link: http://www.cnet.com.au/mp3players/mp...62302-2,00.htm indicates the iPhone has a SNR of 83, some forum posts (http://forums.ilounge.com/archive/index.php/t-3902.html) suggest it is over 90, up to 95. http://download.intel.com/support/mo...45013002us.pdf says the SNR of the D945GCLF2 board is at least 90. So, while conventional thinking would insinuate that PC audio is worse than an iPod/iPhone, doesn't these numbers indicate they are similar, or is this just one piece of the puzzle?
    The sound quality of portable mp3 players is hampered by more than just low signal-to-noise ratio (SNR). Of the links you provided, I would go with the cnet link. The people on the board are just guessting, and he SNR of the DAC chip is useless, because the cheap analog output stage probably is contributing more noise. That being said, SNR isn't critical in a car because the road/engine noise will always be worse than a reasonable SNR (ground loops and alt. whine are a different story). Portable mp3 players also have non-flat frequency response curves (the cnet site didn't show the curve), and this is probably at least slightly audible. Also, there are appears to be quite a bit of distortion reported by the cnet test, worse than the noise floor, in fact. HOWEVER, if you're happy with the way it sounds then who cares about all his stuff.

    SG

  8. #28
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    Stereo mic is good, when you use stereo hardware, for high directionality...good for the noisey car!
    But that's still an awefully noisey (97dB) signal to noise ratio.
    For example, my Xonar's are 119dB SNR...which doesn't sound like a lot of difference, but remember, every 3dB, your doubling the measurement (i.e. 20dB is twice as loud as 17dB). 22dB difference is HUGE!!! Over 7X more noise....

    I like the voltage selectable outputs...that's a nice touch.
    24bit/192KHz is ample sampling, but it's likely STILL compressing the signal...

    I use my onboard Realtek HD sound...for input only. Microphone (which it has echo cancelling) and HDRadio on the line in...works perfectly for that.

    But for music, if you plugged my $8 desktop speakers into that (and my onboard sound), then into my Xonar's (analog), you can EASILY hear a difference....
    Food for thought...

  9. #29
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    Today I tested my build in my car and was impressed.
    I'm using my motherboard's on-board sound which is a Realtek ALC888.
    Playing a CD the computer sounded significantly better than my head unit. Not only that, but there was no distortion at high volumes and without tweaking the gain on my amps, my decibel meter was reading a 4 db increase over the head unit.
    When I finally put the computer in my car for good, I wouldn't be surprised to see it get an additional 10 decibels without distortion. Nice.

    I now fully support the no head unit idea.
    My Nearly Complete Car:
    http://www.mp3car.com/vbulletin/show...ed-car-pc.html

    Micro Control Center... Control Your Car Across the Internet
    http://www.mp3car.com/fusion-brain/1...-internet.html

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  10. #30
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    Now go back to this 'advisor'/saleman and tell him you think he's a ****in' idiot!

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