For Audiophiles (Continued)
Intermodulation Distortion (IMD)
Before I get to this point, let's take a step back and take a look at a basic electrical signal. Most of us only see a signal as a signal - a single line with lots of bumps going up and down. Then Fourier (the bane of my life) came along and found out that signals are composed of multiple parts in the frequency domain. In laymen's terms, a signal is actually comprised of a spectrum of sub-signals at different frequencies. With that in mind, let's get back to IMD.
Intermodulation distortion is generally the result of two or more parts in the frequency domain mixing up with each other and either changing the existing frequency or adding one that was never there in the first place. IMD is generally treated in the same way as total harmonic distortion, rated as a percentage. In fact, it usually comes in the form of IMD+Noise since noise is an ever constant and random addition. Like total harmonic distortion, the lower the percentage of intermodulation distortion, the better.
I usually find myself talking about this in a networking environment but it doesn't make this any less important to an audiophile. Simply put, crosstalk is the problem of a signal on one channel or conductor jumping onto the other. It's what happens when you use a phone and hear "ghosts" talking on it. Obviously, mixing up all those channels is baaaad. If you wanted it that way, you would have bought a crossfeed.
Like most values in signalling, crosstalk is measured in decibels (dB). The higher this number (in negative), the better, because it means that the channels are better isolated from each other and are less likely to leak audio from one channel into another.
Dynamic range is something that most of us have never heard of growing up, Then suddenly, this race for dynamic range started and all hell broke loose. From Dynamic Contrast Range to High Dynamic Range, we've been bombarded by this catch phrase ever since. Most of us probably still don't understand what dynamic range is, even with all that marketing blitz. So, I'll give it to you in plain English.
Dynamic range is generally the range between the smallest and largest representable values with the same average distortion. Here's an example. A range that goes from 1 to 100,000 has a larger dynamic range than a range that goes from 1 to 100. Yeap, it's as easy as that. Of course, the higher the range, more values you can represent and you get better detail, clarity, blablablah. To summarize, the higher this number, the better. Dynamic range is measured in decibels (dB).
DC Blocking Capacitors
When it comes to audio, anything with a DC voltage can very easily destroy your nice pair of speakers or headphones. This DC voltage on the output is called DC offset and all sound card manufacturers implement some form of DC blocking through the use of electrolytic capacitors. In theory, capacitors should let AC through and block DC, so it should be all fine and dandy. Well, this is the real world and not everything is as what it should be.
A reasonably detailed picture of the sound card should be enough to check. Trace the output from the jack inwards and it should hit a capacitor. That, my friends, is the DC blocking capacitor which lies in the signal path. Okay, what is so bad about this capacitor anyway? Well, unlike some other type of capacitors, electrolytic capacitors are not truly linear, especially within the audio spectrum. As such, they tend to degrade sound quality.
However, the clincher is that no two capacitors are built alike. So, what you should look for here are quality capacitors made by reputable brands like Nichicon, Elna, Rubycon, Fujitsu, Nipponchemicon, Matsushita and other manufacturers. Quality capacitors are essential for good audio quality.
If the DC offset is low, you can actually remove the capacitors for better audio quality. Just measure the voltage between ground and the output of your choice using a multimeter. If you get a value below 15 mV, you can generally remove the capacitors. Just remember to bridge over the removed capacitors.