Messages in this thread | | | Date | Thu, 12 Jun 2008 15:03:16 +0200 | From | "Vegard Nossum" <> | Subject | Re: ALC883 recording troubles... |
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Hi,
On Thu, Jun 12, 2008 at 12:49 PM, Takashi Iwai <tiwai@suse.de> wrote: > At Wed, 11 Jun 2008 20:00:17 +0100, > Daniel J Blueman wrote: >> >> On Tue, Jun 10, 2008 at 6:59 AM, Takashi Iwai <tiwai@suse.de> wrote: >> > At Mon, 9 Jun 2008 20:59:00 +0100, >> > Daniel J Blueman wrote: >> >> >> >> Hi Takashi-san, >> >> >> >> I'm experiencing DC offset with the microphone on 2.6.24 (Ubuntu 8.04 >> >> LTS x86-64). I can see on Audacity that the DC offset that varies with >> >> the recording capture level. >> > >> > Could you elaborate? The mic bias level could be changed via the pin >> > control value. Usually, it's set as VREF 80%. >> >> When the recording->capture level is set to 0, the mic has no DC >> offset as expected. Maxing the recording->capture level, the mic input >> is saturated, in between, we see a linear connection.
I find that a good way to examine the captured PCM is the following command:
$ arecord | od -t x1z -v
With the "Capture" and "Digital" controls both at 0 in alsamixer, this outputs just a constant 0x80 byte. This seems natural.
With "Digital" at 0, changing "Capture" has no effect. However, with "Capture" at 0 and these values for "Digital":
db gain -30 byte read 0x80 db gain -28 byte read 0x81 db gain -26 byte read 0x82 db gain -22 byte read 0x83 db gain -19 byte read 0x84 db gain -17 byte read 0x85 db gain -15 byte read 0x86 db gain -13 byte read 0x87 db gain -12 byte read 0x88 db gain -11 byte read 0x89 db gain -10 byte read 0x8a db gain -9 byte read 0x8b db gain -8 byte read 0x8d <-- up two here db gain -7 byte read 0x8e db gain -6 byte read 0x90 db gain -5 byte read 0x92 db gain -4 byte read 0x94 db gain -3 byte read 0x97 ... db gain 12 byte read 0xff db gain 13 (and up) byte read 0x00 <-- seems to flip over or get capped
If I now change "Capture" to have dB gain 0 (35% in alsamixer), I get this instead (for different values of "Digital"):
db gain -30 byte read 0x80 db gain -29 byte read 0x85 ... db gain -18 byte read 0x90 ... db gain -12 byte read 0xa0 ... db gain -6 byte read 0xc0 ... db gain -1 byte read 0xf2
So in fact, if both controls are at dB gain 0 (or one of them is higher), the only byte I can read is 0x00.
> You can try to adjust VREF value of mic pins. > For example, the node 0x18 and 0x19 correspond to the rear and front > mics, respectively. Then run the following as root: > > # ./hda-verb /dev/snd/hwC0D0 0x18 SET_PIN_WID 0x21 > > which will change the widget 0x18 (rear mic) to input-VREF 50% > (0x21). The original value is input-VREF 80% (0x24).
I tried to do this for my card. For me, I need the 0x19 widget, which is the internal mic:
Node 0x19 [Pin Complex] wcaps 0x40008b: Stereo Amp-In Amp-In caps: ofs=0x00, nsteps=0x02, stepsize=0x4f, mute=0 Amp-In vals: [0x00 0x00] Pincap 0x083724: IN Detect Vref caps: HIZ 50 GRD 80 100 Pin Default 0x99a30941: [Fixed] Mic at Int ATAPI Conn = ATAPI, Color = Unknown DefAssociation = 0x4, Sequence = 0x1 Misc = NO_PRESENCE Pin-ctls: 0x24: IN VREF_80 Unsolicited: tag=00, enabled=0
And I tried various values for the PinCtl. 0x20, 0x21, and 0x22, (0x24 was the default), but with no change in the input byte stream AT ALL! And I double-checked, my input source is set to "Internal Mic". (Just to be 100% sure, I tried all three input sources, but it was the same for all. So no change in the input at all.)
Do you have any more tips that I can try out?
Also, I am just curious, is it possible to break the microphone (or other physical components) by changing the voltage levels to unsupported values, or is it safe to experiment freely? I read this in the HDA specification:
"The VRefEn field encoding selects one of the possible states for the VRef signal(s). If the value written to this control does not correspond to a supported value as defined in the Pin Capabilities parameter, the control must either retain the previous value or take the value of 000, which will put the control in a Hi-Z state and prevent damage to any attached components."
Thanks!
Vegard
-- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036
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