A7N8X-DLX Mic Input Noise Level Inquiry

Discussion in 'Asus' started by Kylesb, Sep 14, 2004.

  1. Kylesb

    Kylesb Guest

    I have a nifty WAV editor program that came with Nero that indicates
    the signal-noise ration (S/N) on the Mic input as being pretty poor
    with the Mic boost enabled. I also see the Granted, the Mic boost is
    merely amplifying the input, but with Mic boost enabled, I see only
    about 35 dB S/N on the Mic input with or w/o a Mic plugged in. I see
    about -35 dB on the recording display with the Nero wav editor with
    the "record" mode active. Anyone see similar readings?

    When I disable the Mic boost, the noise level drops, yet one channel
    still has about 8 dB more noise than the other. This symptom appears
    to be identical with both of the A7N8X-DLX mobos that I own so I don't
    think it's PS noise. The box that has the more expensive PS actually
    has more noise on the Mic input w/o any Mic plugged in. Just some
    observations to ponder and discuss.
     
    Kylesb, Sep 14, 2004
    #1
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  2. Kylesb

    Paul Guest

    http://nforcershq.com/forum/viewtopic.php?t=49133

    1) Mute all the analog inputs you can.
    2) Remove four pin audio cable from any CD/DVD that runs to the mobo.
    3) "Enabling Digitalize Input with NV Mixer seems to fix the problem"
    from the thread above.

    It is obvious that onboard sound is a "best effort" kind of design
    for the motherboard manufacturers. In other words, if the design
    engineer came to his status meeting and said "the board is done, but
    the AC97 sound noise floor sucks big time and I've got to fix it",
    you can imagine the managers saying "Ship it!". Motherboards never
    have audio specs, and there are very few review sites equipped to
    try to characterize them. That is why we get crap for audio.

    Here is another thread with more reasons for background noise.
    If you have to go to this much trouble to get decent sound
    performance, a cheap sound blaster is a much easier route.

    http://nforcershq.com/forum/viewtopic.php?t=29255

    Paul
     
    Paul, Sep 15, 2004
    #2
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  3. Kylesb

    Kylesb Guest

    | In article <>, "Kylesb"
    |
    | > I have a nifty WAV editor program that came with Nero that
    indicates
    | > the signal-noise ration (S/N) on the Mic input as being pretty
    poor
    | > with the Mic boost enabled. I also see the Granted, the Mic boost
    is
    | > merely amplifying the input, but with Mic boost enabled, I see
    only
    | > about 35 dB S/N on the Mic input with or w/o a Mic plugged in. I
    see
    | > about -35 dB on the recording display with the Nero wav editor
    with
    | > the "record" mode active. Anyone see similar readings?
    | >
    | > When I disable the Mic boost, the noise level drops, yet one
    channel
    | > still has about 8 dB more noise than the other. This symptom
    appears
    | > to be identical with both of the A7N8X-DLX mobos that I own so I
    don't
    | > think it's PS noise. The box that has the more expensive PS
    actually
    | > has more noise on the Mic input w/o any Mic plugged in. Just some
    | > observations to ponder and discuss.
    |
    | http://nforcershq.com/forum/viewtopic.php?t=49133
    |
    | 1) Mute all the analog inputs you can.
    | 2) Remove four pin audio cable from any CD/DVD that runs to the
    mobo.
    | 3) "Enabling Digitalize Input with NV Mixer seems to fix the
    problem"
    | from the thread above.
    |
    | It is obvious that onboard sound is a "best effort" kind of design
    | for the motherboard manufacturers. In other words, if the design
    | engineer came to his status meeting and said "the board is done, but
    | the AC97 sound noise floor sucks big time and I've got to fix it",
    | you can imagine the managers saying "Ship it!". Motherboards never
    | have audio specs, and there are very few review sites equipped to
    | try to characterize them. That is why we get crap for audio.
    |
    | Here is another thread with more reasons for background noise.
    | If you have to go to this much trouble to get decent sound
    | performance, a cheap sound blaster is a much easier route.
    |
    | http://nforcershq.com/forum/viewtopic.php?t=29255
    |
    | Paul

    I should have mentioned I did my tests with all inputs disabled except
    for a single recording source. This appears to be the way the mixer
    software is designed to function, only 1 recording source can be
    enabled at a time (I recall other sound cards, particularly SB16
    cards, would allow recording from multiple sources, I think).
    Enabling "digitize input" subjects the input signal to the processing
    of the digital audio circuits/drivers. Enabling "digitize input" may
    make the noise better or worse depending upon your equalizer and
    "environment" settings.

    I can't recall if I have the 4-wire CD audio cables installed in this
    box.

    The noise floor is not awful, on the contrary, it's decent or lower
    than -50 dB which gets the noise floor down where one will not hear it
    above typical computer fan noise or room noise. But, the mic boost
    clearly raises the noise floor 20 dB, which is to be expected since
    it's simply an amplification of the mic input signal.

    I did notice tonight while playing with the 3com NIC (which has been
    disabled for some time, but I'm using it for a brief span for some
    testing purposes) that a network speed test using Sisoft Sandra
    resulted in identifiable noise in the headphones I was using during
    the brief burst of data, and I never noticed any such noise with the
    Nvidia NIC. The Nforce thread you linked above where users suggest
    some cures is humorous in a way, b/c each users seemed to find the
    magic fix to noise, e.g., paper washers, using only the 3com nic,
    using only the Nvidia NIC, disabling a PCI bus service,
    enabling/disabling "digitize input", etc.

    It is clear the multifunction LSI circuits that include onboard sound
    face huge design hurdles in establishing a low noise level. In
    addition, the location of the audio signals in the mobo (near the CPU)
    puts those signals in a very noise environment. However, I thought to
    get and use the Dolby Digital trademarks, certain performance levels
    were required in the S/N area, or maybe I am mistaken.

    I'll have to have a look at my system with the SBLive 5.1 and see if
    it's noise floor is any better, just a sec. . . . (/me fiddles with
    sblive 5.1 card in an older K7S5A based 1.4G Tbird system)

    No doubt about it, the SBLive card is much better in the noise floor
    area, the mic input had lower than -70 dB reading with no mic plugged
    in and "mic boost" enabled, and "line in" noise floor was less
    than -60 dB level (I do have the "line in" jack connected to a stereo
    receiver at the moment as I'm recording old LPs and making MP3s
    therefrom, so that might explain the difference in noise floor there).
    One observation I note, the SBLive board has a good quantity of very
    small electrolytic caps, typically used for noise filtering in audio
    circuits.
     
    Kylesb, Sep 15, 2004
    #3
  4. Kylesb

    Paul Guest

    I should have mentioned I did my tests with all inputs disabled except
    for a single recording source. This appears to be the way the mixer
    software is designed to function, only 1 recording source can be
    enabled at a time (I recall other sound cards, particularly SB16
    cards, would allow recording from multiple sources, I think).
    Enabling "digitize input" subjects the input signal to the processing
    of the digital audio circuits/drivers. Enabling "digitize input" may
    make the noise better or worse depending upon your equalizer and
    "environment" settings.

    I can't recall if I have the 4-wire CD audio cables installed in this
    box.

    The noise floor is not awful, on the contrary, it's decent or lower
    than -50 dB which gets the noise floor down where one will not hear it
    above typical computer fan noise or room noise. But, the mic boost
    clearly raises the noise floor 20 dB, which is to be expected since
    it's simply an amplification of the mic input signal.

    I did notice tonight while playing with the 3com NIC (which has been
    disabled for some time, but I'm using it for a brief span for some
    testing purposes) that a network speed test using Sisoft Sandra
    resulted in identifiable noise in the headphones I was using during
    the brief burst of data, and I never noticed any such noise with the
    Nvidia NIC. The Nforce thread you linked above where users suggest
    some cures is humorous in a way, b/c each users seemed to find the
    magic fix to noise, e.g., paper washers, using only the 3com nic,
    using only the Nvidia NIC, disabling a PCI bus service,
    enabling/disabling "digitize input", etc.

    It is clear the multifunction LSI circuits that include onboard sound
    face huge design hurdles in establishing a low noise level. In
    addition, the location of the audio signals in the mobo (near the CPU)
    puts those signals in a very noise environment. However, I thought to
    get and use the Dolby Digital trademarks, certain performance levels
    were required in the S/N area, or maybe I am mistaken.

    I'll have to have a look at my system with the SBLive 5.1 and see if
    it's noise floor is any better, just a sec. . . . (/me fiddles with
    sblive 5.1 card in an older K7S5A based 1.4G Tbird system)

    No doubt about it, the SBLive card is much better in the noise floor
    area, the mic input had lower than -70 dB reading with no mic plugged
    in and "mic boost" enabled, and "line in" noise floor was less
    than -60 dB level (I do have the "line in" jack connected to a stereo
    receiver at the moment as I'm recording old LPs and making MP3s
    therefrom, so that might explain the difference in noise floor there).
    One observation I note, the SBLive board has a good quantity of very
    small electrolytic caps, typically used for noise filtering in audio
    circuits.[/QUOTE]

    But this is not your typical "noise filtering" problem.

    First of all, the AC97 codec does the digitizing. Transmission from the
    Realtek chip (ALC650?) on the left of the board to the Southbridge, is
    done digitally over the AClink.

    The noise problem will exist from the audio connector rack in the I/O
    area, to the AC97 codec. Now, I looked at two A7N8X family boards, and
    I can see audio signals travelling on the surface of the board. This makes
    them "antennas" for noise, and is a definite no-no. They should be routed
    stripline, with solid ground plane over top of them, to protect against
    E fields. Also, there should be sufficient clearance between them and any
    H fields, like the transformers for the Ethernet interface.

    The whole Asus nforce2 layout is compromised by the dual channel memory
    interface. It pushes the processor socket and Northbridge too far to the
    left, and forces other circuits to be placed sub-optimally. If you want
    to see a better layout, compare an A7N8X board to the Abit NF7-S (the
    first one I grabbed).

    http://www.abit-usa.com/images/products/NF7_S_large.jpg

    Notice how the DIMMs are much closer to the front of the computer,
    the Vcore power circuit is pushed North, away from critical routing
    areas near the I/O panel. The area south of PCI5 has been used for
    chips/headers. The layout is less crowded where the audio chip lives,
    and there is more opportunity to treat the audio right. (I wish I had
    a hi res picture, to be able to see more of it).

    If you remember the early history of the A7N8X, Asus did lose their
    SoundStorm "sticker", and who is to say why. It could be those very
    things, like measured noise floor and quality of implementation.

    Imagine how good a board like this could have been, if an extra two
    routing layers were available. Adding 2 more layers of copper adds
    10% to the cost of the PCB board blank, but it would have allowed
    that huge copper "rats nest" between the Northbridge and the DIMMs
    to be compressed, and allowed the use of ground fill around circuits
    that really needed it.

    Also, the audio circuit is powered by a small linear regulator. In
    theory, this is supposed to clean up power to the circuit, but I've
    been taught that in fact a switching power supply can be cleaner
    than a linear regulator. The linear regulator rejects noise well at
    low frequencies, but not at high frequencies, and the +12V used to
    power the regulator, is bound to be dirty after travelling half way
    around the board, to get to the audio circuit. Yet, I don't see any
    RLC filters feeding the regulator, to improve its output.

    So, there are a bunch of things that could be done differently. As the
    board is intended for budget AMD applications though, it is hard to
    do the job right. The NF7-S layout proves there is room for
    improvement, in terms of general layout issues.

    A sound card, on the other hand, has no compromises in its design.
    Plenty of room on a PCI card, to do an audio function, without
    messing it up.

    Paul
     
    Paul, Sep 15, 2004
    #4
  5. Kylesb

    Kylesb Guest

    | In article <>, "Kylesb" <>
    wrote:
    <snip>
    |
    | But this is not your typical "noise filtering" problem.
    |

    I was not very specific in my capacitors/noise filtering comments, but
    plenty of caps are typically used to filter the rail voltages in good
    audio circuits, I was not intending to suggest in-line "audio
    filtering" circuits. That was the intent of my comment about the
    electrolytics. Yes, I understand the audio inputs are supplied to a
    codec that xforms audio into digital data.

    | First of all, the AC97 codec does the digitizing. Transmission from
    the
    | Realtek chip (ALC650?) on the left of the board to the Southbridge,
    is
    | done digitally over the AClink.

    I agree entirely with your observations, if you place audio circuits
    into a digitally noisy environment, special consideration must be
    given to noise filtering, the placement of PCB runners and shielding.

    | The noise problem will exist from the audio connector rack in the
    I/O
    | area, to the AC97 codec. Now, I looked at two A7N8X family boards,
    and
    | I can see audio signals travelling on the surface of the board. This
    makes
    | them "antennas" for noise, and is a definite no-no. They should be
    routed
    | stripline, with solid ground plane over top of them, to protect
    against
    | E fields. Also, there should be sufficient clearance between them
    and any
    | H fields, like the transformers for the Ethernet interface.
    |
    | The whole Asus nforce2 layout is compromised by the dual channel
    memory
    | interface. It pushes the processor socket and Northbridge too far to
    the
    | left, and forces other circuits to be placed sub-optimally. If you
    want
    | to see a better layout, compare an A7N8X board to the Abit NF7-S
    (the
    | first one I grabbed).
    |
    | http://www.abit-usa.com/images/products/NF7_S_large.jpg
    |
    | Notice how the DIMMs are much closer to the front of the computer,
    | the Vcore power circuit is pushed North, away from critical routing
    | areas near the I/O panel. The area south of PCI5 has been used for
    | chips/headers. The layout is less crowded where the audio chip
    lives,
    | and there is more opportunity to treat the audio right. (I wish I
    had
    | a hi res picture, to be able to see more of it).
    |
    | If you remember the early history of the A7N8X, Asus did lose their
    | SoundStorm "sticker", and who is to say why. It could be those very
    | things, like measured noise floor and quality of implementation.

    As a relative latecomer to the A7N8X product line, I was unaware Asus
    lost their "sticker", yet it's not hard to understand why given the
    results of a few simple S/N tests.

    |
    | Imagine how good a board like this could have been, if an extra two
    | routing layers were available. Adding 2 more layers of copper adds
    | 10% to the cost of the PCB board blank, but it would have allowed
    | that huge copper "rats nest" between the Northbridge and the DIMMs
    | to be compressed, and allowed the use of ground fill around circuits
    | that really needed it.

    Adding $10 to the cost of a mobo could sound the death knell w/r/t the
    sales volume thereof. However, if the company paid attention to
    marketing the board properly, an added $10 might be easy to extract
    from consumers if the board delivered superior performance in the
    on-board audio arena. Asian rim companies often times are clueless on
    how to best market their products to the US consumer, imho. If it's a
    DLX version, then by golly, it oughta get all the bells and whistles
    and superior design features.

    |
    | Also, the audio circuit is powered by a small linear regulator. In
    | theory, this is supposed to clean up power to the circuit, but I've
    | been taught that in fact a switching power supply can be cleaner
    | than a linear regulator. The linear regulator rejects noise well at
    | low frequencies, but not at high frequencies, and the +12V used to
    | power the regulator, is bound to be dirty after travelling half way
    | around the board, to get to the audio circuit. Yet, I don't see any
    | RLC filters feeding the regulator, to improve its output.

    Filtering the output of the linear ps is my preferred approach,
    specifically 1 uF filter caps at every IC power connection pin to help
    reduce high frequency noise. When designing audio circuits in years
    gone by, I much preferred using linear supplies as no matter what the
    situation, switching circuits will cause noise in the voltage rails.
    In fact, a design I worked on years ago with microprocessor controls
    and lots of audio circuits used a quality linear PS for all the audio
    circuitry and a separate switching supply for the microprocessor
    circuits to achieve 96 dB S/N ratios throughout. Heh, it was amazing
    what we could do at that time with a 2-3 Mhz clock speed CPU, lol (an
    8085 CPU was used to drive a VF dot matrix display, it was a 4 channel
    audio analyzer used in audio output testing of radio and cassette tape
    products, it even performed wow and flutter tests on tape decks).

    |
    | So, there are a bunch of things that could be done differently. As
    the
    | board is intended for budget AMD applications though, it is hard to
    | do the job right. The NF7-S layout proves there is room for
    | improvement, in terms of general layout issues.

    I guess the DLX board is still considered budget, even with the higher
    price. Guess I'm getting spoiled with the price of things these days.

    |
    | A sound card, on the other hand, has no compromises in its design.
    | Plenty of room on a PCI card, to do an audio function, without
    | messing it up.

    As always, your comments are worthy of note Paul.
     
    Kylesb, Sep 15, 2004
    #5
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