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Remarkable features of Skype

Sound issues on Skype for Windows due to NGC audio codec

NGC is a new audio codec used for Skype-to-Skype calls and it is designed to replace the previous codec SILK, that once replaced its predecessor SVOPC. Abbreviated from “Next Generation Calling”, the new Skype audio codec is still in the testing stage (I think so because it’s activated randomly), but already noticed that during a NGC call, compared to SILK one, the voice sounds much cleaner without background noise and interferences.

But like any new technology, sometimes NGC does not work properly, and due to it during Skype calls may occur various sound issues (like sound interruptions, lack of sound, sound suppression, disabling Sterio Mix and other). As a rule, problems are related to the hardware, drivers or third-party software, and I will give some tips on how to solve them.
  1. First of all be sure that you use the latest version of Skype for Windows, since only the latest versions provide patches and fixes for detected errors.

  2. Next, be sure that you always use the latest drivers for your sound card, microphone and other sound devices. On the other hand, if sound issues started to occur after you have installed the latest drivers, as a workaround is roll them back.

  3. If the previous tips do not help you, try to uninstall any software designed to process and handle your computer sounds (like recording and changing your voice, applying sound effects and other).

What to do if the sound issues still present?

  1. First, you need to make sure that is really a problem with NGC audio codec. To do this, during a call analyze technical information and look for the Technology=NGC value — if it is not present, then your issue is not related to the NGC and you need to find another solution. Otherwise, keep reading.

  2. If the problem really related to NGC, and you have already tried all the options to fix it, at this moment you have two workarounds:
    1. Install Skype (safer, but less features)
    2. Disable NGC (all features, but dangerous)

How to disable NGC?

At this moment, there is no official way to disable NGC, but you can do it in the following way:
  1. Exit Skype
  2. Open folder: C:\Program Files (x86)\Skype\Phone
  3. Rename file RtmCodecs.dll to something else
  4. Launch Skype and make an audio call
  5. Check if issue still exists
Be aware, that this hack may break your Skype and you should use it at your own risk. I know a case when the web camera Logitech C920 shutdowns while trying to switch to 1080p (Full HD) video mode during a Skype video call. If you encounter such problems, rename back the RtmCodecs.dll file.

What is the “RtmCodecs.dll” file?

I may be wrong, but seems this file contains functions that add support for NGC codec (and most likely, for many more other functions). When “RtmCodecs.dll” is missing, Skype uses default audio codec named SILK. I renamed this file and did various tests, and did not notice any problems during audio and video calls, as well as for group calls. That’s why I beg to inform me if on your system something broke down or does not work properly after renaming this library.

Should my interlocutor also disable NGC?

No, because NGC is activated only when all call participants supports it. That’s why even in a group call will be used SILK codec if one user has disabled NGC or uses an unsupported OS or old Skype version.

What problems occur most often due to NGC?

  • No sound during audio calls, but everything works perfectly for video calls.

  • Only the caller’s voice is heard while any computer sounds (including movies, music, and games) are muted.

  • Contrary to previous issue, can be heard only the computer sounds, without the interlocutor’s voice.

I would be grateful for any further details and comments about the article, as well as for reviews of what issue do you had and how you solved it (any technical details are welcome).


  1. 1 +1 0
    you did it , all its fix it right now .

    Thanks so much for the Info about it , its really useful !

    Have a wonderful Day !
    1. 0 0 0
      Hey! Thanks for your feedback. You are always welcome! If you encounter any problems after renaming “RtmCodecs.dll”, please let me know.

      ps. For our readers, please note that our discussion with DivTech begin here, and the problem arose only during audio calls.
  2. 0 0 0
    dr tal,
    The ngc codec has a nasty habit of skype's lazy dev team. to get better echo cancilation ngc takes all audio that is heard from the speaker that skype outputs and ignores it no matter how loud the audio is. or wether its stereo mix or nothing else.

    So the same audio from a different speaker same volume level will play fine but stereo mix unless its stereo mix from a different audio source wont work.

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