Xonar ST/STX mods...

[Coris]

Originally Posted by BKSL

How i can disable digital filter in PCM1792 chip which is used in this audio card ?

Digital filter control, as some other internal controls of the DAC is possible only by software (internal registries). You need an I2C interface to set up accordingly the (in this case) registry 20. You may find in the chip datasheet more details.

[BKSL]

I know this, already. Question is: How set this register in windows enviroment ? :-)

[Coris]

I`m afraid that is not very easy... You have to get very deep into the Xonar driver... to modify it, or you may write a new one. There is the driver which control/program the functioning of the DAC registry. Actually is the CMedia processor which maybe store a software to control that registries. I do not know very well how is build the logic of the software system of this board.
To be honest, I think a such task it may be so time consuming and an enormous work for someone who do not do this as usually, that is not worth in this case.
There are some more simple mods which it push this sound card on very high quality level, than only bypassing that inside the chip digital filter... Actually is not known exactly if that filter is in use or not by the existing driver...

[BKSL]

After few hours of study I solved that it is not possible with this audiocard because hardware.
Digital filter can be bypassed but format of input data to DAC must be changed to "right-justified audio format" for correct function. Asus AV100 (OxygenHD CMI8788) chip supports only "I2S format" :-(.

[hollowman]

Originally Posted by Coris

I`m afraid that is not very easy... You have to get very deep into the Xonar driver... to modify it, or you may write a new one. There is the driver which control/program the functioning of the DAC registry. Actually is the CMedia processor which maybe store a software to control that registries. I do not know very well how is build the logic of the software system of this board.
To be honest, I think a such task it may be so time consuming and an enormous work for someone who do not do this as usually, that is not worth in this case.
There are some more simple mods which it push this sound card on very high quality level, than only bypassing that inside the chip digital filter... Actually is not known exactly if that filter is in use or not by the existing driver...

Well, we can always write/email Asus to allow for more software control of the decoder and/or DAC chip. IAC, I'm sure some designers at ASUS are scanning message boards and threads for future ideas for their devices Maybe the innate "DIYabilty" of opamp rolling was result of customer demand? So, wanting more DIY in the software "domain" is only reasonable. And I don't think it would be all that hard for Asus to release an update of their "Xonar Essence Audio control" software with options that offer direct parametric control of the PCM1792...maybe under an "Advanced" menu.

In another thread, I was specifically discussing this issue WRT the sampling rate and fast/slow filters. On that note -- via Xonar Essence audio center -- has anyone (Corvus5?) graphed 16/44 "upsampled" to 48k, 96k, 192k?

[Corvus5]

The Asus made the opamp upgrade pack with LM49720NA. It may be considered as upgrade for a lot of people. It's not very good. I inserted them hour ago. Top end still to soft, missing precision, no details. LM49860 is a little better, but people may look for some tube amp sound. 49720 gives a bit of it. Still, I don't like it. Asus however decided to release the upgrade pack with 49720. Maybe due to many forum posts. Maybe even someone from Asus is posting here ;-)

Hollowman, the easiest access is to the CS2000 on the ST card. The PCM1792 and CS2000 however on this card the the I2S while the STX PCM1792 has the exclusive access to the I2S. Writing to the CS2000 is very easy from the driver source code at it looks like this:

    oxygen_write16(chip, OXYGEN_I2S_A_FORMAT,
               OXYGEN_RATE_48000 |
               OXYGEN_I2S_FORMAT_I2S |
               OXYGEN_I2S_MCLK(data->h6 ? MCLK_256 : MCLK_512) |
               OXYGEN_I2S_BITS_16 |
               OXYGEN_I2S_MASTER |
               OXYGEN_I2S_BCLK_64);

The access to the PCM1792 is also easy and there are a lot bits to set:

    oxygen_set_bits16(chip, OXYGEN_GPIO_CONTROL,
              GPIO_INPUT_ROUTE | GPIO_ST_HP_REAR |
              GPIO_ST_MAGIC | GPIO_ST_HP);
    oxygen_clear_bits16(chip, OXYGEN_GPIO_DATA,
                GPIO_INPUT_ROUTE | GPIO_ST_HP_REAR | GPIO_ST_HP);

Writing data is also easy. I pasted most interesting part:

static void update_pcm1796_oversampling(struct oxygen *chip) {
(...)
pcm1796_write_cached(chip, i, 20, reg);
}

The CS2000 is programmed for clock dividing by 2 or 4 and I mentioned this already before. Then we get the 32000, 44100 and 48000. Without CS2000, the CMI8788 has to do the work.

Going back to the I2S format:

    .dac_i2s_format = OXYGEN_I2S_FORMAT_I2S,
    .adc_i2s_format = OXYGEN_I2S_FORMAT_LJUST,

I don't know if the PCM1792 will support filter registry setting change through the I2S :-)

[Corvus5]

The interesting in the PCM1792 for the user to control is:
1. Digital attenuation control: 0 dB to –120 dB and mute, 0.5 dB step
2. De-emphasis control: Disabled, enabled
3. Attenuation speed selection: ×1fS,×(1/2)fS,×(1/4)fS,×(1/8)fS
4. Stereo DF bypass mode select: Monaural, stereo
5. Digital filter rolloff selection: Sharp rolloff, slow rolloff
6. Digital-filter bypass control: DF enabled, DF bypass.

Playing with the slow rolloff may be nice. By default the PCM1792 uses sharp rolloff. This may cause a lot of phase errors.

[BKSL]

Hi Corvus5, how can be done settings change in Windows ?

[hollowman]

Originally Posted by Corvus5

Hollowman, the easiest access is to the CS2000 on the ST card. The PCM1792 and CS2000 however on this card the the I2S while the STX PCM1792 has the exclusive access to the I2S. Writing to the CS2000 is very easy from the driver source code at it looks like this:

CS2000? Don't you mean AV100? The CS2000 is simply "Clock Generation and Multiplication/Jitter Reduction Solution".

Why are you bringing a totally different card (HT Omega) into this discussion?
Stick to the Asus Xonar ST/STX which uses PCM1792.

[Corvus5]

HT Omega? I've never heard of it. What is it?

The AV100 is the Asus name for the CMI8788 used on Xonar Essence ST. The CMI8788 on the ST controls the CS2000 with the proper software. It also controls the PCM1792 using the same I2C line. I don't know why the Xonar Essence ST driver uses functions for the PCM1796. Maybe the control method is the same so the functions remained the same.