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

[Hui Wang]

On 06/11/2015 09:15 AM, 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.
>>
>>
> Do your codec revision support this mono out volume ?
>
> 7.4.31.AFG (NID = 01h): DAC3OutAmp (Mono Out Volume)
I looks like the current driver does not use this to control the volume.
>
> How do you assign the two volume control to headphone, speaker and
> subwoofet ?
speaker and headphone are assigned to DAC0 (nid: 0x13), they use the DAC 
amplifier to control the volume.

subwoofer speaker is assigned to DAC1 (nid: 0x14), it use the DAC 
amplifier to contorl the volume.

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