[alsa-devel] 2 speakers are assigned to the same DAC, this can't support 4.0/2.1 channles

[hwang4]

On 2015年06月10日 09:30, Raymond Yau wrote:
>>>> I am trying to enable the subwoofer speaker on a HP laptop, on this
>>>> machine, there are two speakers and one headphone, but the BIOS verb
>>>> only enabled one speaker(nid 0xd) and one headphone(nid 0xb), I need
>>>> to use quirk in the kernel driver to configure the second speaker
>>>> (subwoofer speaker, nid 0x10). Under current alsa driver, the
>>>> headphone will be assigned a dac (nid 0x13) and the 2 speakers will
>>>> be assigned a dac (nid 0x14), this assignment is not good since 2
>>>> speakers share the same dac, this means 2 speakers can't work
>>>> at the same time to support 4.0/2.1 channels.
>>>>
>>>> On another Dell machine with realtek codec, there are also 2 speakers,
>>>> 1 headphone and 2 dacs, on this machine, 1 speaker and 1 headphone are
>>> assigned
>>>> 1 dac, and the other speaker is assigned another dac, so there is no
>>>> problem for this machine to support 4.0/2.1 channels.
>>>>
>>>> Through debugging, I found on Dell machine, the speaker nid only has
>>>> one connection to dac (hardwired), so when driver assign dac to it, the
>>>> map_single() can successfully assign the each dac to the 2 speakers
>>> respectively.
>>>> But on that HP machine, the speaker has multiple connections for dac,
> the
>>>> map_single() can't work for this machine.
>>>>
>>>>
>>>> The alsa-info.txt for that HP machine is at
>>> http://pastebin.ubuntu.com/11667947/
>>>
>>> Refer to 92HD91, you don't need 4 channel when there is band pass filter
>>> for the subwoofer at the mono pin
>> Yes, you are right.
>>
>>> 2.2. Mono Output
>>> The Mono Out port source selection, power state, and mute characteristics
>>> are all independently
>>> controlled by the mono output port controls. EQ does not apply to this
>>> path. An internal 2nd order band-pass filter is provided to restrict the
>>> output frequencies when using mono out to drive an exter-
>>> nal amplified sub-woofer
>> Where did you find this text? Does it mean there is a hardware low
> frequency pass filter inside the codec?
>
> http://www.temposemi.com/products/pclaptop-hd/92hd91/
>
> 2.3. Mono output Band-Pass Filter
> For many applications, the primary speakers are incapable of reproducing
> low frequency audio. Therefore it is desirable to implement a woofer or
> sub-woofer speaker. The mono output is ideal for this task. However, the
> frequency response should be restricted to prevent interference with the
> primary speakers. Typically an external filter, known as a cross-over
> filter, is used. The mono processing path includes a band-pass filter with
> programmable high and low cut-off frequencies to eliminate the need for an
> external filter.
>
> 2.3.1. Mixer Filter Description The band-pass filter is derived from the
> common biquadratic filter and provides a 12dB/octave roll-off. The filter
> may be programmed for a -3dB lower band edge of: 63Hz, 80Hz, 100Hz, 120Hz,
> 150Hz, 200Hz, 315Hz, or 400Hz.
>
> The filter may be programmed for a -3dB upper band edge of: 150Hz, 200Hz,
> 250Hz, 315Hz, 400Hz, 500Hz, 630Hz, or 800Hz.
>
> The band-pass filter is enabled by default with a cut-off frequencies at
> 120Hz and 250Hz. The filter may be bypassed using the associated verb
> (processing state verb
Thanks very much, very useful information.


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