EC25 sampling rate 16kHz

IoT Modules LTE Standard Module
1

Dear forum,

I am using a few EC25. In the area I am located most cell phone provider offer higher quality voice calls.

When using the EC25, document quectel_eg060keg120k_series_voice_over_ttyusb_application_note_v1-0.pdf tells to use sampling rate (rate) to 8 kHz, and format (format) to 16-bit linear.

I saw that competitor SIMCOM on similiar placed products (SIM7600) supports also 16 kHz sampling rate.

Through this I expect the audio quality should increase. If I sent higher quality audio between the host controller to the lte modem module, the modem module probably also use a higher quality for the modem connection to the provider if offered.

Do you plan to support higher quality audio on Quectel EC25 series?

Best regards
Chang

2

Dear forum,

I am really interested in this to find out.

I could succesfully enable VoLTE. I verified this by free qcsuper application to record diagnosis logs. Due to software limitation I was not able to see IMS traffic directly, but could see that the gsmtap message are different and that the voice connection is different. However the audio quality is still not great and I wonder if it is due to the sampling rate of 8kHz.

Best regards, Chang

4

I tried to set QDAI. It was +QDAI: 3,0,0,4,0,0,1,1 and I changed it to +QDAI: 3,0,0,4,0,1,1,1 but audio was distorted. I am sure I the correct sampled data (16kHz) as input.

So how to do it? Is this possible in a newer firmware?

Quectel
EC25
Revision: EC25EUXGAR08A17M1G_20.200.20.200

5

Hi @tne
When a recommended codec is selected and 16 kHz sampling rate is desired, please input
. Currently only ALC5616 supports 16 kHz (AT+QDAI=3,0,0,5,0,1,1,1).

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image876×834 85 KB

1 Like
7

Dear @lyman-Q ,

thank you very much for your response to my post. It seems we looked in a different AT Commands Manual or an older version. We do not remember that we saw the notes number 6 in the document we read.

Thanks for pointing us to it.

We use the Quectel mini PCIexpress cards with the EC25. We changed now the QDAI initialization. We read it out and it is exactly like your post stated, 4096 kHz Clock frequency and 16 kHz Sampling rate.

We tried with software reset but also with a complete power off the full system.

send (AT+QDAI?^M)
expect (OK)

+QDAI: 3,0,0,5,0,1,1,1

OK
– got it

send (AT+CFUN=1,1^M)
expect (OK)

We adjusted the software communicating via USB with the EC25 and changed
from “audio slin (16 bit Signed Linear PCM)” to “audio slin16 (16 bit Signed Linear PCM (16kHz))”

Normally this would be it, but we face distorted audio in both directions.

What is interesting: with the adjusted +QDAI: 3,0,0,5,0,1,1,1, the audio is OK if we keep sending in our software the slin (16 bit Signed Linear PCM). Like before with the default +QDAI: 3,0,0,4,0,0,1,1,

This makes us believe that the EC25 is not using the new setting? We use Revision:
C25EUXGAR08A17M1G_20.200.20.200

Do you have any other idea? Is there some other setting needed via AT commands?

Big thanks for any idea you might have and which helps us, Chang+Mario

9

To summarize: The settings +QDAI: 3,0,0,5,0,1,1,1, has the same behavior as +QDAI: 3,0,0,4,0,0,1,1,
Providing 8kHz sounds for both configurations sound ok. 16kHz is always distored. We can rule out that we do not provide the correct sample data because then I would expect that +QDAI: 3,0,0,5,0,1,1,1, with provided 8kHz should be distorted, which is not.

So it seems the settings is just not applied or evaluated by the modem correctly.

The device was rebooted 10sec after setting QDAI with AT+CFUN=1,1. After next startup the QDAI setting was read out and equal to what was set before the reboot.

10

Hi @tne
May I ask if the slic you are using now is model ALC5616? If it is not this model of slic, it does not support the 16k sample rate, I think that is why the 16k sample rate distortion is set.

1 Like
12

Dear @lyman-Q ,

we are using the following 2 parts:

On the quectel page I could not directly download the PCB or specification. SixFab HAT made the schematics available. I checked all components but I could not find ALC5616 or a similiar IC part of the SixFab HAT. So I think the ALC5616 is then part of your product. Is this correct?

I read before that the ALC5616 is the default for EC25. So I guess it is populated on the Quectel LTE EC25 MINI PCIE.

Also the factory setting of QDAI on the EC25 MINI PCIE was ALC5616.

Is my assumption correct that I use the ALC5616? How to find out otherwise?

Best regards,
Mario

13

Link to LTE EC25 Mini PCIe: LTE EC25 Mini PCIe series | Quectel

photo_2024-11-07_12-35-36
photo_2024-11-07_12-35-361280×720 135 KB

14

Hi, my current understanding is that the ALC5616 is an external audio codec? For the application we are using we do not use analog audio input which uses an external audio codec to the quectel modem. Instead we want to use Audio over USB or VoLTE over USB.

See also the first post. We refer to the PDF for this use case in the initial post. Your USB Audio spec says 8kHz is only supported, while other manufacturers support 16kHz for similiar product. Can you please tell us if you support 16kHz on USB Audio? We would like to order more devices but audio quality is not good enough. Therefore which products you have which support 16kHz on USB audio?