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PCM2902b Annoyance

Intellectual 310 points

Replies: 12

Views: 10365

i know there is no way (execpt at rom mask level) to change the USB terminal type from 0x0201 (microphone) to something better for my application... like (0x701) Radio Receiver, heck even a line in would be better
0x201 causes windows vista and windows 7, to make it the default recoding device on initial plugin

terminal type 0x0201 doesnt even make sense when somone would use the SPDIF in, no mics are SPDIF :)

I would also love to disable the output interface... so that doesnt even show up.... (and take over playback device on WINDOWS on inital plugin)

im basicly using the 2902 as INPUT ONLY for hd radio receiver (after setting up windows, it does work great)

Question... it doesnt seem documented, two pins SEL0 and SEL1 (what do they do?, if anything)... would be cool if could have it set some defaults... how about sel0 disables OUT ENDPOINT TERMINAL

oh it would be great if this IC had a full eepom (with not just VID/PID, but other settings for dsabling output or input(some people only use it for speakers!)

oh another thing, on XP, the device enumerates with NO level or mute control avail... for the input terminal, very odd...



  • Hello Mitchell,

    My name is Dafydd Roche, I'm on the product definition team for next gen audio converters.

    The PCM2902 was before my time, however, I just wanted to say that I really appreciate your feedback, and ideas for next gen products.

    I will forward this question to the development team, and see what feedback I can get.

    Thanks again



  • In reply to Dafydd Roche:


    im glad someone finnally notest my post... im moving forward with my project
    and it is a ISSUE, that the terminal type is 0x0201= Microphone

    causes windows 7 to think its a microphone, when im using it basicly as line in
    (actually in my case a FM Radio terminal type 0x710)

    (man i wish it was optional eeprom, with settings like this... heck id take 0x200 or 0x0603)

  • In reply to Mitchell Solomon:



    not to mention, that on windows 7, the device is WAAAY too loud, prob windows 7, since it thinks its input is a microphone, is applying some kind of boost



  • In reply to Mitchell Solomon:


    When a microphone is attached to a PC via USB, the audio packets traversing the USB are typically PCM, meaning that audio scaling should have happened _before_ the A/D converstion and the samples are sent by the device.  Sixteen-bit samples from a microphone should thus range between 0x7fff (+32767) and 0x8000 (-32768), for maximum SNR, just like samples from Line In.  So, I don't understand why you think that 'Mic In' would produce significant level differences from 'Line In'.  Can you explain?



  • In reply to Frank Minich:

    your right, i dont know for sure...

    but what i do know is that windows 7, sees the TERMINAL TYPE as microphone, and ITS INCREADBLY TOO LOUD!!!!
    basically making the PCM29xx series almost useless on Windows 7, i have to lower volume to 3 to at least have no distortion

    its possible that windows 7 audio system is applying a BOOST because it thinks its a microphone..
    but there really is no way to test this is the PC29xx series has the TERMINAL TYPE HARD CODED into the descriptor

    ok, even if its not an issue with level in the IC, the annoying factor that its TERMINAL TYPE is hard coded to microphone
    has other side effect in windows.... if we could change it to say LINE-IN, windows would chose a better icon and description
    since in a lot of cases the PCM29xx isnt connected to a microphone, it would be nice to have this option

    EVERYDAY , i search the web looking for a better solution then the 29xx series, due to thier inherent limitations


  • In reply to Mitchell Solomon:


    Do you see the problem when you connect to a Win XP PC?  That is, is the problem Win7-specific?

    Which PCM29xx part are you using?  Is it possible that your microphone is overdriving its input?

    Can you look at the USB traffic (i.e., using a sniffer)?

    I still find it _extremely_ difficult to believe that the problem is related to LineIn/MicIn.  What comes in over USB should already have been normalized prior-to A/D.



  • In reply to Frank Minich:

    Hold the phone ... another customer has complained in regard to Win7 and has provided their implementation, so we're taking a look at it.

  • In reply to Frank Minich:

    i know this, the ISSUE is not in VISTA!! the volume can be nicely set at 50


    glad you got some info... its so annoying, i get complaints, that my products audio is all destorted... its becuase of the level > 4

    what im thinking its because the terminal type is MICROPHONE, windows 7, is applying a internal BOOST to the audio
    I could be a problem with windows 7, but i would NOT assume that, if i was a mfg i would do EVERYTHING possible
    to see if my product is the issue, or if i can adapt to Win7, and if not, then bring up the issue with Microsoft...
    I have tried 3 differnt products, but all have the pcm29xx product inside, they all have this same problem...



  • In reply to Mitchell Solomon:

    I can confirm that this is a Windows 7 issue.

    The PCM2902 product used on the Window XP platform was, in my case, just the opposite.  The record level needed to be at 100% and even then was a bit on the low side.  


  • In reply to Mike Long:

    It's a Windows 7 only issue. As  PCM290x has no input volume, windows 7 "provides" one. In digital form.

    The samples are just overscaled to produce the gain. To get a satisfactory sound quality, you have to set the recording levet to about 3%.

    Windows 7 also assumes it is a mono input. Windows 7 just assumes too much...

    Has anybody tried this part on Windows x64? I seems to me it doesn't work. At least with the windows native drivers (usbaudio.sys).

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