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Audio Mixer / Multiplexer

C
Expert 2065 points
Other Parts Discussed in Thread: PCM1865, PCM1863, PCM1861, PCM1863EVM

Hi everybody. 

I am currently involved in a project where we have to mix between 1 to 3 audio signal together and then encode evereything in MP3 format (like a karaoke: mic one side, line in in the other side, and then record). We need to be able to start the encoding / recording in MP3 while we shoudl be able to switch on/off the 1 to 3 audio line in.

So let's say for example, we have one line with a mic (signal 1 for voice) and another line with line in (signal 2 for music), we need to superpose (mix) both together to make one single signal (like a karaoke) in order to encode the resulting signal.

Can you advice which component and configuration could be used ? the device will work on battery

I was thiking to use an analog audio mixer ic which i could pilot the input with a few GPIO to decide which signal go trough the mixer. what do you think about it ?

Regards

 

  • 0
    TI__Genius 9175 points

    Hello,

    We have a few ADC parts which feature input mixing and individual channel gain controls. These would be our PCM1861 (hardware controlled) and PCM1863 & PCM1865 (software controlled).

    The digital output language is also selectable so you could find an MP3 converter that would mate well with it.

    Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Expert 2065 points

    Hello, 

    Thanks for your feedback. I am a bit confused about if we should use hardware or software control. Can you clarify ?

    What we try to do is this: The key on the left control the left entry to be recorded or not, and the key on the right is controling the right entry.

  • 0 in reply to C
    TI__Genius 9175 points

    Based on your application, I would recommend the software controlled PCM1863 or PCM1865 depending on the number of channels you need.

    With software control, the entry key can be sent to the MCU. Once the MCU detects that it has been triggered, an I2C burst of traffic can then control the PCM1863/5. This can be used to reconfigure the gain, mixing, and mute functions for the desired channel.

    For example if you wanted to remove one of the audio sources, when you toggle the control key for that source, you can then remove it from the mixed single output channel as a method of muting. Or, you could reduce the gain if desired.

    The PCM1863/5 are very configurable parts through I2C commutation which writes the control registers. These registers determine the functionality of the part.

    Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Expert 2065 points

    Hi Mat, 

    I attach the block diagram of what I have in mind. There is a  MCU (probably MSP 430) commanding mixer to choose which source will be recorded by the MP3 encorder. We have mic 1 and mic 2 and earphone line as possible source. The press button on the left side will command via the MCU which source should be recorded

    1./ This is for on battery application so I wanted to verify the PCM1861 is appropriate for this kind of application and confirm how you would see this? I see the PCM familly being very rich in functionnality (hence costly..) so I was wondering if there were another IC more suitable?

    2./ I am wondering how to deal with the stereo mode coming from the line in? we don't need to record in stereo in our case (we don't care about it actually, so in this case how to deal with it), should we just pick one wire

    Thanks in advance for your time. :)

  • 0 in reply to C
    TI__Genius 9175 points

    Hello,

    The PCM186x family is not designated for portable applications. However, its power consumption is still very respectable at 85mW (PCM1861/3) or less for 3.3V sources. Take a look at page 9 in the datasheet to see if it meets your requirements.

    The point of using a PCM1863 is that you can use the mux and mix features to mix all of the input stereo channels into mono within the PCM1863 part. I would recommend ordering a PCM1863EVM and trying the features with the GUI.

    The issue with the PCM1861 part is it has no mixing features or fine gain tuning. Since it is hardware controlled, the part was simplified for standalone operation.  The PCM1863/5 are I2C controlled so these parts have more features and can be adjusted on the fly.

    Although these parts are more expensive, it will significantly simply the signal path since it can do everything you need in a single device.

    Regards,

    Matt

  • 0 in reply to Matthew Beardsworth
    Expert 2065 points

    what do you advice then for portable device ?

  • 0 in reply to C
    TI__Genius 9175 points

    I would still recommend the PCM186x series. It has all of the functionality you want and low power consumption. There is a GUI you can work with the EVMs for evaluation.