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Can I change the PCM2707 IC S/PDIF output volume by setting the IC volume control HID commands thru its SPI bus?

Radosvet B.
Intellectual 490 points
Other Parts Discussed in Thread: PCM2706C, PCM2706, PCM2704C, PCM2705C, PCM2705, PCM2704, TUSB2036

Hello,


I already read the PCM2707 (-C) datasheets, but the information given there is not fully clear.


1.   Can I change the PCM2707 (2707C) IC S/PDIF output volume by setting the IC volume control HID commands thru its SPI bus?

The OS used – Win’ XP, iOS.

The iPhone, iPod can be used too.

iPhones work with the PCM270x chips:

https://hifiduino.wordpress.com/2013/06/15/apple-airport-express-usb-audio-output-mod/
Apple Airport Express USB Audio Output Mod

http://blog.jdslabs.com/?cat=57


2.   What does mean the “Master volume control” mentioned in the
datasheet on the page 27? :

======================================
The built-in digital volume controller can be manipulated by an
audio-class-specific request from 0 to –64 dB in
steps of 1 dB. Changes are made by incrementing or decrementing one
step (that is, 1 dB) for every 1 / ƒS time
interval, until the volume level reaches the requested value. Each
channel can be set to a separate value. The
master volume control is not supported. A request to the master volume
is stalled and ignored. The built-in digital
mute controller can be manipulated by an audio-class-specific request.
A master mute control request is
acceptable. A mute control request to an individual channel is stalled
and ignored. The digital volume control
does not affect either the S/PDIF or I2S outputs (PCM2706C/7C only).
======================================

3.   Again, what does mean ” The digital volume control does not
affect either the S/PDIF or I2S outputs (PCM2706C/7C only).”

So, the S/PDIF output volume by setting the PCM2707 volume control
commands thru its SPI bus will be operated in PCM2706/7 or not?

The "only" point is not clear here.  "Only" yes, or only not?


Regards,
R. B.

  • 0
    TI__Guru** 104335 points

    Hi R. B.

    PCM2707C SPI connection is used to modify the USB descriptors. Some information about the possible descriptor changes is on page 21 through 23 of the datasheet.
    The volume control is not accessible through SPI connection.

    The volume setting is controlled for each channel individually. As shown in the figure below, each channel volume is accessible through balance volume control. When the volume slide or the HID control is modified both channel volume controls are modified.

    The digital output (S/PDIF) volume can not be controlled as it is designed to be used as line level output signal. Only the analog output volume can be controlled.
    The "only" is referring to the digital output interface (I2S or S/PDIF). Only the PCM2706C and PCM2707C have digital audio interface while PCM2704C and PCM2705C does not.

    I hope this answers your questions properly. Please let me know if there are any doubts.

    Best regards,
    -Ivan Salazar
    Texas Instruments

  • 0 in reply to Ivan Salazar
    Intellectual 490 points

    * The volume control is not accessible through SPI connection.*

    Why?

    The PCM2707 datasheet states:
    =================================
    Table 8. SPI Register Field Descriptions :

    D6 Reports volume-up HID status to the host (active high)
    D6 Reports volume-up HID status to the host (active high)
    =================================


    * The digital output (S/PDIF) volume can not be controlled as it is designed to be used as line level output signal*

    When I change the foobar2000 PC player volume slide, S/PDIF level is changing.
    I use the PCM2705 IC.


    * Only the PCM2706C and PCM2707C have digital audio interface while PCM2704C and PCM2705C does not.*

    Again, why?

    I use the PCM2705 IC and it has S/PDIF digital audio interface.

    P. S.

    Ivan, would you please help with this topic too:

    Can the PCM2704…PCM2707 USB input signals be active applied when IC is unpowered?

    https://e2e.ti.com/support/data_converters/audio_converters/f/64/t/515117

    I have not still got a correct answer there.

  • 0 in reply to Radosvet B.
    TI__Guru** 104335 points
    R. B.

    I'm very sorry for the confusion.
    Actually volume HID status can be controlled through SPI on PCM2705C and PCM2707C. But it is unable to control the digital interface volume.

    I think the digital interface volume can be controlled from software like foobar and win media player, but the HID status controls and volume slider on windows only modify the analog path volume. There is a previous discussion about this in the following link: e2e.ti.com/.../942384

    Regarding the last question, I must have said that only PCM2706C and PCM2707C have I2S digital audio interface while PCM2704C and PCM2705C does not. Actually all PCM2704C through PCM2707C have S/PDIF digital audio interface but the sentence in the datasheet is referring to the I2S output.

    I will take a look at the post from the link.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 490 points

    OK.

    Thank you, Ivan.


    1. Can you say that the MUTE function thru PCM2706/07 SPI or switch-buttons is not operated for the IC digital outputs (S/PDIF, I2S) just like the digital volume control too?

    2. Where will be changed the PCM2707 IC output analog volume if I set a PCM2707 SPI command to change volume +/- level?
    In the PC OS, PC software player or inside the IC PCM2707 itself?
    I. e. where this “volume regulator” is when I use IC SPI volume control commands?

    3. Should I left open, pullup or pulldown the PCM2704C/05C IC HIDx/SPI (22…24 pin) inputs, if I do not use them at all?
    Are they have internal pullups/pulldowns or so?


    R. B.

  • 0 in reply to Radosvet B.
    TI__Guru** 104335 points
    R. B.

    1. This is correct. MUTE does not operate on digital output, just like the volume control.

    2. SPI commands works the same as HID pins. The volume change is reported to the host OS and then comes back to modify the analog volume in the IC. The volume step is 1-dB . The volume variation is relative to the actual volume level and it can only be incremented or decremented, it is not allowed to set a specific volume level.

    3. Pins 22 through 24 can be left floating if not used. There are internal pulldown on these pins.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 490 points

    Thank you, Ivan.


    Please see the PCM2704/2705 application schematic.
     
     
    The IC (PCM2704 or 2705) used as a USB--> S/PDIF converter only, the IC DAC section is not used.
     
    The IC is used in self-powered mode.
     
    The circuit supply voltage is switched off/on as 0/3.3VDC.
     
    The SSPND suspend output is used to switch on/off the output digital section supply voltage.
     

    1.   What can you say about the design total correctness?
     
    2.   Is the design solution for IC HOST input correct?
    Can you propose some solutions (w/o to use a MCU)?
     
    3.   Can you recommend to use a RC-filter (22 Ohms + 22pF) on the USB lines, as it is on this schematic?

    4.   Can I change the DT (pin 3) line 1.5kOhms pullup resistor to its 10kOhms value?


    Regards,
    R. B.

    P. S.

    Ivan, can you help with this topic?:

    Can the PCM2704…PCM2707 USB input signals be active applied when IC is unpowered?

    https://e2e.ti.com/support/data_converters/audio_converters/f/64/t/515117

  • 0 in reply to Radosvet B.
    TI__Guru** 104335 points
    R. B.

    I apologize for the delayed response. I will take a look at this and come back with an answer today.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Radosvet B.
    TI__Guru** 104335 points
    R. B.

    I think C57 and C58 may not be necessary and I think there should be no problem changing R96 from 1.5-kOhm to 10-kOhm.
    D+ pull up resistor should be connected to VDD and it is connected to 5-V through BC847.
    The rest of the schematic seems to be fine.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 490 points

    Hello, Ivan,


    * I think C57 and C58 may not be necessary*

    Look at the TUSB2036 USB hub IC Figure 9. TUSB2036 Bus-Powered Hub, Ganged-Port Power-Management Application in the datasheet.
    ==============================
    An optional filter capacitor of about 22 pF is recommended for EMI suppression. This capacitor, if used, must be placed between the hub terminal and the series resistor, as per section 7.1.6 of the USB specification.
    ==============================

    You can find such an information and in the TUSB2046, 2077 datasheets, www.ti.com/.../sllu190.pdf (Figure 5. TUSB2036 EVM Schematics), www.ti.com/.../sllr047.zip (in all the files included)…


    Why do you think that those filters “may not be necessary”?


    * D+ pull up resistor should be connected to VDD and it is connected to 5-V through BC847.*

    So what's wrong?

    See the PCM2705C datasheet (p. 26):

    ===============================

    D+ should be pulled up with a 1.5-kΩ (±5%) resistor. To avoid back voltage in self-powered
    operation, the device must not provide power to the pullup resistor on D+ while VBUS of the USB port is inactive.

    ===============================


    What is the difference with the solution from the picture posted?

    The 1.5k pullup will be connected to the +D line when the +5V USB power is connected and the +3.3V self-power is ON.

    It’s not true?



    Regards,
    R. B.

  • 0 in reply to Radosvet B.
    TI__Guru** 104335 points
    R. B.

    The capacitors at the D+/D- lines are recommended for edge rate control and to filter the high frequency noise (EMI). Our PCM20x EVM's do not use these capacitors because these are relative simple systems and are designed in such a way that there should not be any distortion problem at D+/D-. Although if EMI or a possible issue with these lines signal integrity is a concern, it would be better to keep using these capacitor filters.

    Regarding the pullup resistor at D+, I mean that it is connected to +5V but is should be connected to VDD = 3.3V instead.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Intellectual 490 points
    *Although if EMI or a possible issue with these lines signal integrity is a concern, it would be better to keep using these capacitor filters.*

    EMI is really everywhere.


    * Regarding the pullup resistor at D+, I mean that it is connected to +5V but is should be connected to VDD = 3.3V instead.*

    Why?

    Would you clarify this?

    As I understand, there should be the good U (+D) "1" line level enough when the HID device is attached.

    Does the solution not to do that?


    Regards,
    R. B.
  • 0 in reply to Ivan Salazar
    Intellectual 490 points

    *Regarding the pullup resistor at D+, I mean that it is connected to +5V but is should be connected to VDD = 3.3V instead.*

    I understand you.

    But I do not understand why it should be in that way you said.

    The 1.5k pullup will be connected to the +D line when the +5V USB power is connected and the +3.3V self-power is ON.

    Regards,
    R. B.