Tech Tip: Troubleshooting Audio

Description: Troubleshooting Your Audio.



Ever since Diamond Multimedia introduced the consumer to one of the first MP3 players about 15 years ago, the digital music scene has become a necessity to the common consumer. Starting at that point, you could take tracks from your favorite CDs and transfer them to a portable media player to enjoy the music on the go. Granted, you could only fit about 8-10 songs on the first mp3 players, but the concept was amazing! So what can you do to get the most out of your digital music - whether it be coming from your smartphone, Mac, PC, or digital audio player? What other formats are out there? How do you make sure the quality is as good as it can get?

A Few Things You Should Know
When we say that a format is lossy, it tells us that it will destroy information to achieve a small file size. When we say lossless, a smaller file size is achieved WITHOUT destroying any information from the original file (similar to how a zip file operates). 

Example: A three minute song takes roughly 30MB on your hard drive when it is ripped from the CD. When your conversion software (i.e. iTunes) makes a MP3, the file size goes down to around 5MB. Considering that the new file is about 1/6^th the size of the original, this is amazing!

Chart of Common Audio Formats

Audio Format	Lossy or Lossless?	Where Have I Seen This?
MP3 (MPEG 1/2 , Layer 3)	Lossy	DRM-Free Music Stores, Internet Radio, Converted CD’s from iTunes/Windows Media Player
AAC (Advanced Audio Coding)	Lossy	Pandora, iTunes
WMA (Windows Media Audio)	Lossy	Xbox Music, Rhapsody
Vorbis	Lossy	Spotify, Many PC and Console Games
FLAC (Free Lossless Audio Codec)	Lossless	(archival purposes)
APE (Monkey's Audio)	Lossless	(archival purposes)
SHN (Shorten)	Lossless	(archival purposes)
WAV/AIFF	No Compression	Retail Audio CDs

Put On Your Thinking Ears

So you've hooked up your Smartphone/Tablet/Portable Device/Computer to some speakers, and the sound that is coming out is awful. What do you do? First off, let's analyze the sound and make some mental notes to help you out later.

1. Is it too soft?
2. Does the sound come in and out at random points?
3. Does the audio sound scratchy during louder sections?
4. Does the band sound like they're playing underwater?
5. Is there any aspect of the music or characteristic that is missing? (assuming you are familiar with the music already)
6. Do cymbal crashes (or other high frequencies) sound artificial, muddy, or loose?

Did your observations match up with points 1, 2, or 3? If they did, then you should start troubleshooting the speakers themselves. If it's too soft (or not heard at all), your volume is probably set too low. Make sure the volume is set to a reasonable level in Windows. To avoid this issue, always keep your computer at maximum volume and only use your speakers to adjust the volume to your liking. This also avoids hiss in the speakers, because they're not trying to amplify a weak signal. If you experience sound fading in and out or you still do not hear anything, double check your speaker connections to make sure there's nothing loose. The connections are usually color-coded (see right). For a set of stereo speakers, you would use the green connection only. If you have surround sound, you would be using the black and orange connections as well. If the connections are good, then you may have a problem with the amplifier in the speakers. If the audio sounds scratchy during loud sections, you probably have the volume set too high on your speakers. This is called distortion. One thing to watch out for is sometimes individual applications may have a separate volume control that is independent of the system (i.e. VLC). This can get complicated, because now you have three separate volumes to keep track of, and three possible chances for distortion. If turning the volume down all around doesn't fix it, then the original recording may be distorted, and there's nothing that can be done to help that.

Did your observations match up with points 4, 5, or 6? If they did, then your troubleshooting should start with the source and not the speakers.

4. Where did your music come from? Was it downloaded from the internet? Did you make the file yourself from a CD? Did it come from an online music store? Not all music is of the same quality that comes from the Internet. The real question is what is the quality of the file you are listening to? Sometimes, the media player will report the quality of the file (in kbps) as shown below.
   
   
   (Windows Media Player example)

If you don't have this feature, an easy way to guess the quality is to find the length of the song (in minutes). Now find the actual file (on the hard drive) and determine how big the file is. In windows, you can right-click the file and click properties to see the file size. On a Mac, you would right-click the file and click Get Info.



In this example, the song, Kalimba, has a length of 5:48, and its file size is 8.02MB. In this case, size (8) is greater than length (5). You can assume that the quality of the audio is good or excellent if the file size is larger than the length. If you find that your file is about 5 minutes long but is only 4-5MB, you can conclude that the quality of the file is probably not very good, which is why you might think it sounds bad.

Why Does Bitrate Matter So Much?

Bitrate is extremely important. The higher the bitrate is the more information can be retained from the original file. Since seeing is believing, what follows on the next page are a few spectrograms. Don't be afraid! These psychedelic pictures represent all of the sound frequencies used in a particular audio file over a specified amount of time. Each graph has two separate pictures to show you the left and right channels (since it is a stereo audio file).


Left: Original CD and Right: Compressed MP3 (128kbps)

The biggest difference between the original and compressed files is the rather abrupt cut-off of frequencies we see in the MP3 version. Everything past 16,000 Hz is gone. The simple logic behind this is that the encoder needs to get rid of things in order to reduce file size. Another way that the encoder can reduce file size is by eliminating sounds that we may not have noticed in the first place. A classic example is when a loud and soft sound are heard at the same time, the encoder will eliminate the softer sound (if possible). Sometimes the encoder may choose to eliminate certain frequencies that we may not be able to hear that well. These decisions are modeled around human hearing and the encoder is aware of what most people can and cannot detect. The lower the bitrate, the sloppier these decisions are, which is why we think it sounds bad. The higher the bitrate, the more sophisticated these decisions are, making them harder to detect, which is why we may think it sounds good. Some of these decisions are hard to see on the graph and are better left for the ear to decide.

As a closing thought, please remember that your speakers are there to play back what you give them. If you feed them a bad source, they'll play the bad source-simple as that. Also please remember that a truly decent set of speakers will cost you some money. You can't expect a $20 pair of speakers to knock your socks off. The speakers are not always at fault! Please consider the source!

For more assistance contact Technical Support here.