EVAL-ADAU1761Z to run all ANALOG AUDIO INPUTs?

Hi Kelvin,

The ADAU1761 has 2 ADC channels to convert the 4 analog inputs. In order to use all of the analog inputs on the device, you must program the mixer, shown here is Figure 32 on Page 29.

http://www.analog.com/static/imported-files/data_sheets/ADAU1761.pdf

Have you downloaded and installed SigmaStudio? Are you able to connect the software to the ADAU1761?

Best regards,

Coleman

Hi Coleman,

I am now able to input several "ordinary" audio source into the IN1, IN2, IN 3/4, by programming the mixer, as you suggested. Thanks.

But however, I still failed to make an old condenser mic to work in either IN1 or IN2. Any suggestion? My configuration is similar to

Figure 33. Stereo Differential Microphone Configuration

or

Figure 34. Stereo Single-Ended Microphone Configuration

of this document:

http://www.analog.com/static/imported-files/data_sheets/ADAU1761.pdf

Shall I need to connect J15 and J18? What else needs to be done?

Kelvin

Hi Kelvin,

Yes, please apply J15 and J18, and you will also need to use the SigmaStudio interface to enable the MICBIAS function in the IC.

Regards,

Coleman

Hi Coleman,

With your help, it works now. Thank a lot!

However, the overall output level from mic is not large enough, even though I had boosted the micbias to highest and the mic input stage gain to 6 dB, this did not help much...overall situation is, the stereo audio input from the IN 3/4 is quite larger than from mic. I tried two different analog mics, the same situation...I cannot accept current audio quality from the mic1 and mic2 (volume up the final playback stage did not help...it only raise the noise...)

As I will have to have two mics to operate in the same time in parallel with stereo audio input from IN 3/4 (and all need to go to dsp core for digital processing), my questions then are:

1. What can the possible problem is? What place should I check?

2. Can I change the micbias pull up resistors (R7 and R15 on the schematics) to a lower value, such as 1K, to boost the mic level? but without hurting this audio codec chip?

3. Or, I need to find better (or matching ) mic such that they work with the existing circuits? Can you make some suggestion to the selections of such good MEM analog mics that work with ADAU1761Z?

4. Does ADAU1761Z support two digital mics that I can separately adjust with? "Figure 32. Record Signal Path" of the ADAU1761Z.pdf seems to suggest that when digital mic is used, the LAUX / RAUX cannot be used through dsp core any more?

Thanks in advance!

Kelvin

Hi Kelvin,

1) Please refer to the following diagram:

Using LDVOL and LDBOOST, you should be able to get enough gain from the ADAU1761 preamp stage.

2) I do not recommend that you adjust the 2k00 resistor value in the MICBIAS path. Lowering the value will impact the frequency response and noise performance, as well as reduce the signal level.

3) With regards to MEMS microphones, please look here:

InvenSense | MEMS Sensor System on Chip | MEMS Microphones

4) You are correct about choosing between the inputs. If you turn on the digital mic inputs, you will not have access to the analog inputs. Please refer to Page 31 of the ADAU1761 datasheet:

http://www.analog.com/static/imported-files/data_sheets/ADAU1761.pdf

Regards,

Coleman

Hi Coleman,

I have found post stating that the digital and analog inputs can and can't be used simultaneously on the ADAU1761...

you state above that :4) You are correct about choosing between the inputs. If you turn on the digital mic inputs, you will not have access to the analog inputs. Please refer to Page 31 of the ADAU1761 datasheet:

http://www.analog.com/static/imported-files/data_sheets/ADAU1761.pdf";

This doesn't make sense to me, since I see so many posts about digital mic and analog in. What am I missing?

Best, Stephen

Hello Stephen,

What may be confusing here is that perhaps some of these posts are talking about digital inputs as in the serial port. You can use the serial port as inputs to the core and the oversampling ADCs will feed the decimator and then go to the core so both the digital inputs via the serial ports, and the ADCs will be available. However, when using a PDM digital microphone it is a different story. The PDM mics are also oversampling (1-bit) converters and require a decimator to obtain multi-bit output at the core sampling rate. There is only one stereo decimator which is shared between the ADCs and the PDM Digital Microphone inputs.

So if you need both then you will have to use either an external ADC or an external PDM input processor. The ADAU1372 is a quad ADC and can also bring in four PDM microphones and output them as a serial digital signal that you can bring into the 1761. Then the ADC in the 1761 will still be available.

Another really simple option is to the ADAU7002 which converts PDM signals into I2S that you can bring into the 1761. This is a low cost small footprint solution.

Dave T

Dear Dave,

Thanks so much for your response, I've asked my EE Craig to respond with some questions regarding whether or not the ADAU1777 might be better for our application. We need 2-4 analog ins as well as 2-4 digital mic inputs able to be individually processed simultaneously in parallel.

Over to you Craig...

Best, Stephen

(Please forgive any typos or autocorrects introduced by my iOS)

Hello Stephen and Craig,

Things to keep in mind:

The ADAU1777 can process four signals. They can be four analog mics, four digital mics, or 2 digital and 2 analog. You cannot do more than four and the analog or digital are set in pairs. Plus, this is not a full function DSP. It is really a filter engine to run IIR filters really fast.

Dave T

Thanks Dave - is there another AD DSP closer to our requirements?

Best,

Stephen

(Please forgive any typos or autocorrects introduced by my iOS)

Hello Stephen,

I am not certain I know all of your requirements but I will go with the idea that you require some analog inputs and digital microphone inputs (PDM) is that correct?

We have DSPs that have several digital inputs for PDM mics but no on-chip converters so you would need a codec. So the 1761 is probably still a good choice. You have a lot of analog inputs on that part and I suggest you use the ADAU7002 to convert the PDM microphone to I2S digital and go into the ADAU1761 via the serial port. This is a very low cost solution and the 7002 is a very small and simple part to use.

If you only need stereo analog input then the ADAU1701 is another good choice but I have to step back a little since I really do not know how much DSP processing you need and what you are actually doing with it? Then what are your output requirements? Headphones? Class-D amplifier?

Dave T

Thanks Dave -

Your statement "you require some analog inputs and digital microphone inputs (PDM)" is quite correct and I am copying your suggestions to our engineer, Craig Seyl.

Is it possible for us to have a brief discussion with you by phone regarding our requirements?

We were recently on the cover the Rolling Stone with regard to applying our ADEL hearing technology to allow Brian Johnson to return to the stage with AC/DC, so our application is probably somewhat different than what you might expect.

We were using a CX20889 Wheeler chip from Conexant, but their demands on taking advantage of Brian's huge celebrity status (videoed testimonials, etc.) and lack of full software support led us to checking out your company's devices.

The 1761 has many of the EQ and DRC capabilities I need which the 777 apparently may not have, so the I2s mic suggestion may be the workaround we need.

Please feel free to call me any time on my cell at 303-748-4621 or is there a number I can reach you at?

I know you guys don't ordinarily offer phone support, so I will keep the discussion to simply familiarizing you with our application, ok? Your knowledge of you company's many devices might direct us toward another path.

Best, Stephen

(Please forgive any typos or autocorrects introduced by my iOS)