Unwanted Distortion

The SE215's from Shure are fantastic in ear monitors however like all things they break. Specifically the cable and after it broke. I ordered a replacement, however after I plugged them into my computer for testing I heard a horrible crackling. Damn dodgy cable! Well that's what I thought...

Testing

After testing a different set of headphones (Beyerdynamic DT770's) I quickly realised it was coming from the left channel but the crackling was following the same pattern as the audio file. I tested WAV files, MP3 and Vorbis OGG files. Same thing. Perhaps it's only that specific track or maybe it's the program I am running the file through? Nope! I tried VLC, Spotify and Rhythmbox. Same thing.

Hmm... Maybe it's not the cable and due to my first test I can tell it's not an issue with the left driver in my SE's. Maybe the solder is loose on the headphone jack port? Well I can test that by plugging in my external sound card/audio interface and then my phone, trying both headphones through that. The crackle has gone through the phone but I can still here it through the interface at a high volume.

Drivers

So now I know that it is coming from the laptop not just the port. It must be a software issue. Okay cool, that means I can fix it! Let's think I recently converted from Ubuntu to it's older brother Debian so it's probably whatever audio drivers are installed by default in Debian. Quick search. ALSA and PulseAudio.

ALSA

Is the backbone of the audio in Debian systems. By typing alsamixer into the terminal brings up a terminal “GUI” with a single audio meter but with a searching you are greeted with lot's of meters for: Master, Headphones, Speaker to name but a few. It also gives control of the sensitivity of the input as well (microphone). Alsamixer is very nice but missing a few features in my opinion.

PulseAudio

PulseAudio is what my laptop has defaulted to. It's basically the newer version of ALSA and is very user-friendly with a GUI and the ability to adjust individual programs volumes and routing.

After spending a little while playing with the settings it seems the problem is due to distortion rather than a “crackle”. By turning the audio down it goes away but I like listening loudly ;)

Fixed!

So what to do? By using either the PulseAudio mixer or alsamixer I can see that the headphones output is set to 100% but the main output is only 55%. Aha... So I am causing the headphone to be above 100% causing distortion. So a little more tweaking and the best setting appear to be Headphones set to 100% and Main set to 0 – 35%. These parameters provide enough room to crank it but very little to crackle.

After a little more searching this SOLVES the issue!

#Linux #Debian #Audio #AudioEngineering #ProblemSolving #ALSA #PulseAudio #Fixed

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