i.MX ProcessorsのトピックRe: Continuous noise issue during VOIP call

Continuous noise issue during VOIP call

namanthaker — Thu, 19 Mar 2020 11:29:28 GMT

Hello,

I'm working on IMX8M Mini EVK with Android Pie (p9.0.0_2.3.0) OS.

I have integrated CX9000 synaptics audio amplifier and CX20921 Dual MIC voice processor to the EVK.

There are two DMICs connected on the CX20921, one for capturing left channel data and other for capturing the right channel data. A 10W speaker is connected on the CX9000 speaker amplifier.

The connection between NXP processor, CX9000 and CX20921 are as shown in below diagram.

The CX9000 and CX20291 are detected successfully on the EVK. I am also able to play and record audio on the device using tinycap and tinyplay commands.

Then I created a custom WebRTC based Android application to implement VoIP functionality. Using this app I can connect to other Android based device running the same application. When I tested the VoIP functionality, I hear a repetitive noise on the other end i.e. the other Android device.

I have tested the application with several Android devices like Samsung tablets, Google tablets, mobile phones, etc and the same issue is observed.

When I use the application between two mobile devices or tablets or a combination of those, the noise is not produced. Only when IMX8 EVK is connected to other Android device, the noise is produced.

I also tried using other applications from PlayStore like Linphone and Jitsi-Meet to test VoIP functionality, but the same noise is heard on them too.

For reference I have attached a recording file containing the noise that is heard on the other end.

Audio capture and playback using the default recorder and music applications in Android works fine. No noise is observed while using them. Similarly, no noise is observed during playback/capture through tinycap and tinyplay.

I tested the same use-case on a Qualcomm EVM with Snapdragon 625 processor, but in that device the noise is not observed during VoIP. In this case, the HW connections, Codec drivers and the Android applications used were same as that were used in IMX8MM.

From the above observations, it seems the issue is introduced in the Android framework.

How can I go about to remove the noise during VoIP call ?

Re: Continuous noise issue during VOIP call

sureshrao — Thu, 26 Mar 2020 05:49:21 GMT

Hello namanthaker‌,

Since no noise is observed during the playback/capture with tinyplay/tinycap, I would also suspect issue with mixer settings. Maybe you can check the logcat, it can provide some hints, also dumping the CXxxx registers may help.

Best Regards,

Suresh

Re: Continuous noise issue during VOIP call

namanthaker — Fri, 27 Mar 2020 14:06:38 GMT

Hello Suresh,

Thank you for your answer.
I will check the logcat and dump the registers to see if it helps.

Regards,
Naman

Re: Continuous noise issue during VOIP call

namanthaker — Mon, 30 Mar 2020 12:51:17 GMT

Hello Suresh,

I looked through the logcat but did not find any useful hint.
The logs are attached, can you please give it a once-over and see that I have not missed anything ?

Is the VoIP use-case using MIC, tested with IMX8MM design ? If yes, please provide information about the how the test was performed, what setup was used, commands/application used etc.

Regards,

Naman

Re: Continuous noise issue during VOIP call

namanthaker — Fri, 03 Apr 2020 14:10:48 GMT

Hello Suresh,

Any updated on the this ?

Can you please confirm that you have noticed the noise in the shared audio file "VoIP_noise.m4a" ?

Regards,

Naman

Re: Continuous noise issue during VOIP call

sureshrao — Sat, 04 Apr 2020 14:10:19 GMT

Hi namanthaker‌,

Can you dump the codec configurations for both VoIP, tinyplay?

Best Regards,

Suresh

Re: Continuous noise issue during VOIP call

namanthaker — Mon, 06 Apr 2020 06:40:10 GMT

Hi Suresh,

Please find attached 'tinyplay_registers.txt' and 'VoIP_registers.txt' files for register dump of CX9000 during tinyplay and VoIP call respectively.

For reference, please refer attached screenshot of I2S registers set from datasheet.

Regards,

Naman

Re: Continuous noise issue during VOIP call

sureshrao — Tue, 07 Apr 2020 05:26:46 GMT

Hello namanthaker‌,

Can you try with the default micfil in i.MX8MM?

Best Regards,

Suresh

Re: Continuous noise issue during VOIP call

namanthaker — Tue, 07 Apr 2020 06:04:13 GMT

Hello Suresh,

We tried to connect a DMIC directly to the micfil lines on IMX8MM EVK, but the audio captured does not contain any sound. Please refer attached wav file for the captured audio data.
We connected DMIC clk line on J1003.40 pin and DMIC data line on J1003.35 on the IMX8MM EVK for data capture. We also tried to capture audio after connecting DMIC data line on pin 36, 37 and 38 of J1003 at a time, but none of them worked.

The command used to capture audio:

tinycap file.wav -D 2 -d 0 -b 16 -r 48000 -c 1

We have flashed the default android Pie image 'android_p9.0.0_2.3.0_image_8mmevk' supplied by NXP for this testing.
Please let me know what can be done to capture audio directly using micfil.

Regards,
Naman

Re: Continuous noise issue during VOIP call

jimmychan — Thu, 09 Apr 2020 14:55:38 GMT

If local audio playback and record has no issue, then low level driver should be OK. For VOIP use case, I think you should check the echo cancellation solution.

Another thing should be checked is the playback + record working at the same time. You can measure the bit clock and frame clock to check are they correct at that time.

Re: Continuous noise issue during VOIP call

namanthaker — Mon, 13 Apr 2020 06:39:27 GMT

Hello,

Thanks for your inputs !

In our system the AEC is controlled by CX20921. We in contact with Synaptics for disabling the AEC and checking the use-case to see the impact it has and see if tuning can be performed on it.

1. NXP Host side issue probability reason :

Host Processor	Audio Play Mechanism	Audio Record Mechanism	Test Case: Both Audio Out (play) & In (Record) use case
NXP i.MX8M Mini EVM	Synaptic CX9000	Synaptic CX20921	Periodic Noise Issue is present
NXP i.MX8M Mini EVM	Synaptic CX9000	NXP PDM Direct Input	Periodic Noise Issue is NOT present
NXP i.MX8M Mini EVM	NXP Default Headphone WM5424	NXP PDM Direct Input	Periodic Noise Issue is NOT present
NXP i.MX8M Mini EVM	Bluetooth Speaker	Synaptic CX20921	Periodic Noise Issue is NOT present
QCOM 620 EVM	Synaptic CX9000	Synaptic CX20921	Noise is not present

Table #1

2. Tinycap is working, Where-as VoIP has issue ruled out :
[Test recording is attached here]

Test setup : NXP i.MX8M Mini EVM + Synaptic CX9000 (Speaker) + Synaptic CX20921(Mic)

Test timeline	Actions other than tinycap recording	Add on action	Test Results
00-05 Seconds	No tinyplay	Quiet environment	Periodic noise not observed
06-10 Seconds	tinyplay for 5 sec	Speak 1, 2, 3 (for initial 3 seconds), last 2 secs quite	Periodic noise observed
11-15 Seconds	No tinyplay	Speak 1, 2, 3 (for initial 3 seconds), last 2 secs quite	Periodic noise not observed
16-20 Seconds	tinyplay for 5 sec	Speak 1, 2, 3 (for initial 3 seconds), last 2 secs quite	Periodic noise observed

Table #2

3. B CLK & WS_CLK summary for setup:

Codec	Use-Case	Signal	PAD	Qualcomm Setup	NXP Setup	Clock Source
CX9000	Playback	BCLK	I2S_RX_CLK	3.075 MHz	3.075 MHz	Host
	Playback	WS_CLK	I2S_RX_LRCK	48 KHz	48 KHz	Host
	VoIP	BCLK	I2S_RX_CLK	3.075 MHz	3.075 MHz	Host
	VoIP	WS_CLK	I2S_RX_LRCK	48 KHz	48 KHz	Host
CX20921	Recording	BCLK	I2S_TX_CLK	3.075 MHz	3.075 MHz	Self
	Recording	WS_CLK	I2S_TX_LRCK	48 KHz	48 KHz	Self
	VoIP	BCLK	I2S_TX_CLK	3.075 MHz	3.075 MHz	Self
	VoIP	WS_CLK	I2S_TX_LRCK	48 KHz	48 KHz	Self

Table#3

Summary :

1. As per above Table#1, ROW #1, 2, 3, 4 && Tabel#2, Row#1, 2, 3, 4
It has been evident that noise is present when Synaptic chip AEC feature has been used.

2. However when we compare Tabel#1: ROW#1 & 5, NXP host side issue probability is evident
Please note that Qualcomm based board setup and NXP host based setup has used same Synaptic unit (HW, Firmware and all setting including test environment used, refer below Table#3 for details)
Infect recording using tinycap as well as VoIP call has very good Quality with long range.

3. Due to lockdown we can’t check these clock, whether they are very perfect with more calibrated CROs without going to office labs
To confirm whether the QCOM Vs NXP host provided clocks are perfectly same (i.e. glitches or noise free or not).
Hence does your team can share experience, whether NXP i.MX8M Mini chipset checked/ used with any other ODM with any external Audio CODEC based on I2S data and I2C programming Like Synaptic is being used in our case (Connection being show below, where Voice processor is CX20921).

Indeed, Once we hear inputs from Synaptic, we will let you know the result with AEC disabled.

Meantime can you please check above points.

Regards,

Naman

Re: Continuous noise issue during VOIP call

sureshrao — Tue, 14 Apr 2020 07:26:43 GMT

Hello namanthaker,

From the table#3, the playback clock is provided by Host, the capture clock is provided by CX20921.

From the below image, the playback clock is provided by CX9000, the capture clock is hard to say provided by whom.

I don't know which one is the correct one.

From my experience, to make AEC work, capture and playback clocks need to be synced. But in either case, it can not be ensured that the clocks are synced. The best way to be sure is to measure the clock signal while running VoIP...

Best Regards,

Suresh

Re: Continuous noise issue during VOIP call

namanthaker — Thu, 23 Apr 2020 14:40:09 GMT

Hello Suresh,

Thank you for the continued support!

We successfully managed to remove the continuous noise in the VoIP call. As per your suggestion regarding clock synchronisation, we made changes in the kernel, to use i.MX8MM as master and configured CX20921 in slave mode.

Previous Configurations:
IMX8 as Master and CX9000 as Slave
IMX8 as Slave and CX20291 as Master

New Configurations:

IMX8 as Master and CX9000 as Slave
IMX8 as Master and CX20291 as Slave

We have below queries based on the issue:
Q1. What could be the reason for the noise to be absent when IMX8MM is made master and CX20921 is used in slave mode ? Because, such issue is not observed when in Qualcomm EVM which has the same configurations as our previous configurations i.e. CX20921 as master.

Q2. In our system, we are using 2 individual I2S master for CX20921 and CX9000 respectively. But we plan to connect a single I2S from i.MX8 to both CX20921 and CX9000 with i.MX8 as master. Do you see any issues/ problems or challenges that may arise while using the same I2S ? Are there any restrictions in using the same I2S on IMX8MM?

Regards,
Naman

Re: Continuous noise issue during VOIP call

namanthaker — Wed, 29 Apr 2020 10:19:43 GMT

Hello sureshrao,

Any update on the above queries?

Regards,

Naman

Re: Continuous noise issue during VOIP call

sureshrao — Sun, 03 May 2020 15:45:43 GMT

Hello namanthaker‌,

For Q1, the reason is also unclear to me.

For Q2, There are no restrictions in using the same I2S. One need to ensure I2S modes and parameters set in CPU side should align to CX20921 firmware.

Best Regards,

Suresh