The scenario may differ from user to user. In rare cases, it can also happen out of the blue when you are just doing your routine stuff on your Mac.
What happens is that a Mac OS X blocks system’s volume control functionality because it is usually taken over by the external device (speaker/headphone) or third party software. So one can see why it can be a problem if the external device has no function control volume. Even if it has, controlling the volume through the keyboard can still be very desirable by users such as myself. In this guide, i will walk you through the steps to address this issue.
Method 1: Kill The coreaudiod Process
Go to Finder -> Applications -> Utilities -> Terminal. Click and Open the Terminal Utility.
In the Terminal console, type the follow command, and then your password. The password prompt will be blank, and when you type the password it will still be blank, so without thinking HIT Enter after typing in your password.
Once done, test again to see if the Volume Control works.
The Workaround
This work around may not be as helpful but just for your knowledge, you can also adjust the volume via Terminal. by typing the command below. The number 5 indicates the volume level which you can change/adjust.
Method 2: Disconnect/Reconnect Audio Device
If this issue occurs when you don’t have an external audio device such as headphones connected to the Mac, then what you can do is simply take a pair of headphones or external speakers and plug them into your Mac and then unplug them.
Method 3: Select the Correct Audio Output
To understand the issue more clearly, we’ll see how it actually works. Let’s assume you have a Sharp TV connected to your Mac OS X via HDMI Cable and the sound is not adjustable from the volume control keys, and you’re getting the non-functioning speaker icon when you try to adjust the volume. Click the Apple icon from the top bar (left) and choose System Preferences -> Sound -> Output
Now since the sound output is the SHARP LCD, connected via HDMI cable – if i adjust the volume from the Mac it won’t work, but if i adjust the volume via the LCD then it will work. However, if Internal Speakers are selected as the sound output, then the volume control on the mac will work.
Method 4: If your External Device does not support Volume Control
SoundFlower is free utility which passes audio between different applications. It allows you, for example, to send live audio from applications such as Traktor or Ableton Live into the Mixlr app. Download and install SoundFlower from here. Open Audio MIDI Setup by going to Applications -> Utilities -> and choosing “Audio Midi Setup”
Click the + (Plus Sign) at the bottom left of the screen and Select Create Multi Output Device from the pop up menu.
In the right pane place a check next to SoundFlower (2ch) and the external device you have currently attached or your Internal Speakers if no such device is attached. Then,Right click or CTRL + CLICK on Create Multi Output Device and click Use this device for sound output from the pop up menu.
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