A fix for the issue of phone calls being too loud and the lack of privacy during calls. It's a two part fix, but only phones equipped with a MediaTek chipset can benefit from the second part. Please let me know in the comments or via PM whether this worked for you or not, any ideas of improvement for the current article and your opinions.
Explaining the issue First off let’s explain the issue, because not many people using these phones even realize there is an issue with the in-call sound being too loud. Come think of it, there are few instances in which you get to listen to your phone from meters away (except for when using the speaker function), and this is why the problem goes generally unnoticed. Those who did notice it, though, don’t like it one bit, because the loud incoming sound during calls (the voice of the person on the other end of the line) can be heard by the people in the vicinity even when the in-call volume is set to the lowest value. With the Xiaomi POCO M4 Pro there’s little privacy in this regard and it can lead to at least some embarrassing moments. While using this phone expect sharing your entire phone conversation with the world around you. It's not great. Apparently many Xiaomi phones have this problem, including the POCO X3, Redmi Note 8T and the 12X, which means the issue has been around for a relatively long time (at least 3 years) and still there’s no official fix (e.g. changing the the default volume profile) or acknowledgement. To sum it up, the reasons for the lack of privacy during calls are the build of the phone (with multiple speakers and case openings that allow sound to spill out from the device) and the fact that the incoming call sound is simply too loud, even on the lowest setting. The fix If you value your privacy more than the (sub-par) stereo experience provided by the M4 Pro, then you can do a few things to mitigate the problem. While it probably won’t fix it completely, the results are satisfactory in my opinion. 1. Blocking and re-directing the sound The first part of the solution is quick and, while it might seem outrageous, it actually works. On the top edge of the phone, right next to the headphone’s jack, there is a string of five holes for the top loudspeaker. These holes are facing up while in normal conversation, with the phone held to the ear. As for the earpiece, there is a forward-facing slit (a string of pinholes) where the display meets the casing. It seems that inside the phone, between the two openings, there is no barrier, so the in-call sound exits the phone through both the upward loudspeaker holes and through the forward-facing earpiece slit. I haven’t actually opened up the phone so I can’t confirm if there's an actual earpiece speaker and a loudspeaker, or if there’s only one loudspeaker that also acts as an earpiece speaker during calls. The POCO M4 Pro showing the position of the holes for the loudspeaker and the earpiece. The orange waves indicate in-call sound spilling out through the upward facing loudspeaker holes (bad, undesirable), while the blue arrow indicates the in-call sound coming through the forward-facing earpiece opening (good, normal). Blocking the upward holes will prevent sound to escape in that direction, resulting in the attenuation of unnecessary sound diffusion around the unit and in a slightly higher volume coming through the forward opening. By applying some clear tape over the five upward pointing holes next to the headphone’s jack, you block that route for sounds originating in both the earpiece and the top loudspeaker. I put two strips of clear tape over those holes, forcing the sound to be expelled mostly through the wider and narrower, forward-facing earpiece slit located between the display and the casing, limiting the amount of sound escaping into the surrounding area and thus increasing call privacy. The side effect is that it also directs the top loudspeaker playback sound (music, videos etc.) through the forward-facing slit, though without much difference in quality, and so it seems like a reasonable trade off. The protective cover of the phone (e.g., the silicon cover that came with the phone) can also be modified with tape to further block the corresponding openings. The added benefit of using clear tape is that the modification is almost invisible, but any solid tape should work. While this works okay for the M4 Pro, other phones could fare better or worse in taking advantage of this trick, depending on their speaker configuration and body design. 2. Lowering the volume The second part of the solution involves accessing and modifying internal phone settings. Phones equipped with a MediaTek chipset benefit from a hidden settings panel called the Engineer Mode, which is also the case with the POCO M4 Pro. While accessing and changing the values in this mode is an easy affair, careless alterations of these settings could also potentially damage the phone. Before making any changes make a note of the default values so that you can return the phone to its initial state. The settings we’ll be talking about could affect the speakers of the device if using values that are too high for the speakers to handle. Other settings which we’ll not cover here could pose even more serious threats to the device, so, if you’re not sure what they do, it’s better to leave them untouched.
Here you'll see three drop-down lists and some editable numeric values. The UL Gain value represents the gain of the microphone of your device, or how loud your voice will be heard by the other people over the phone. The default value is 188. For example, if you were to set it to 100, your voice heard by the others during calls will be lower in volume. UL stands for UpLoad (outgoing voice sound). The DL Gain values (11 steps) represent the sound volume from incoming calls. Index 0 is the lowest possible setting, at 64 by default, while Index 10 is the loudest setting, at 160 by default. The defaults are usually way too high in volume, resulting in loud incoming voice volumes in calls and a lot of the sound escaping into the surrounding area (and, maybe, even in hearing damage). So, lowering these values will reduce the volume and pretty much eliminate the issue. DL stands for DownLoad (incoming voice sound).
The work flow could be like this:
The new sound profile should be available immediately after making the modifications, without the need of a reboot. Different results can be achieved by altering the values, but make sure to not set the volume too high (not even by mistake) or you could damage the phone’s speakers or your hearing permanently. Check everything twice before applying the new values. A new volume profile could start at much lower (or higher) values that the default one, and increase at different rates. Probably you can even reverse the slider by filling the values in reverse. In the first try I brought the lowest value to 32 and the highest to 104. This profile has a smaller step between lower values, because volume differences can be noticed more easily in quiet environments, and a bigger step between higher values. If the loudest value is not high enough, it could be further increased, but it’s recommended to adjust the few index steps under it as well in order to retain a nice, consistent volume progression curve. I did this for my second try and I'm happier with the new values. In the following table and graph you can see the default profile for the incoming sound (during calls) and two proposed new profiles, a quiet one and a medium one. I recommend using the medium one, as it starts low enough to keep convos private, but goes high enough for that volume boost you might need when taking calls in noisy environments. You may test the speakers using the built in CIT / FQC Test mode that is accessible by tapping five times on the kernel info from About phone > All specs > Kernel version. Alternatively, you can access the CIT menu by dialing *#*#6484#*#*. Once the menu is open, you can tap Receive and Play music by receiver, two options that will use the handset / earpiece speaker to playback prerecorded sounds at the maximum level of the sound profile. However, these tests have limited relevance and ultimately you should test the new volume profiles in real calls. 3. Increasing the media playback volume If your media playback volume is not loud enough, for some reason, you can increase it from the Engineer Mode. This will probably cause distortion in your speakers and probably damage them over time, depending on how loud you listen on them. For this go to Hardware Testing > Audio > Volume > Audio Playback. I have to say it again: exercise caution when making changes, don't use wild values and stay safe. Ending notes Hopefully this works for you as good as it did for me. Let me know!
Granted, by applying these so called fixes you will lose some of the audio capability of the top speaker for media playback, but you will hopefully gain some privacy during calls. You alone decide which is more important for yourself. Ultimately, you can change the phone altogether. While having this issue with the POCO M4 Pro I was looking at alternatives within the same price range and I couldn't find a phone better suited to my needs than this one. If I could not have fixed it, probably I would have returned it and gotten a Samsung A22 4G instead. I also kind of liked the Motorola G41, but the fact that it came with a shared dual sim / SD card slot was a deal-breaker for me. At the time (March-April 2022) there were limited phone options in this price range and specs, especially with my specific needs: long battery life, dedicated dual sim and SD card memory extension, a compass, decent overall performance and, of course, in-call privacy. Wrote off the entire Xiaomi family and Realme (because I got pretty mad with Made in China on this one), and the potential candidates got narrowed down drastically. This brought me to the Samsung A22 4G, even though I think it's not as good as the POCO M4 Pro 4G: the A22 has slower charging speeds, worse screen in terms of both resolution and brightness, slightly lower overall performance, lack of NFC in some regions and no cover and screen protection included in the package. Have fun! If you have questions, ideas, opinions or comments, go for it!
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