Id say EQ can not change sound quality. An EQ only affects frequency response -- it can not affect anything else in the signal. You can make a track sound better with EQ though, which is done in mixing, mastering and many times the end consumer does it as well.
A cable can not affect the definition, tone, extension or the impact (etc etc) of the bass; either it delivers the signal as it is, or it doesnt (its broken/not working properly and needs to be replaced). To affect those things you need to use effects/filters (not good for quality, unless you want to create a different sound (which you dont want unless you are creating music))) or re-record. You can use EQ to make the bass seem different, but its only a mind trick (youre not doing anything but increasing or decreasing amplitude).
There are several very good (free) VST EQs available.
Ill expand LFFs EQ help-list a bit (for people at "I use presets" level and those you want more technical knowledge):
In graphic (software ones, hardwares can have knobs) equalizers, every bar is called a band. Each band has a frequency or a frequency range. This is the 3 first bands of the Winamp EQ.
- - - - 3+
- - - - 2+
- - - - 1+
-___-___-___- 0-/+ dB
- - - - 1-
- - - - 2-
- - - - 3-
70 180 320(hz)
Frequency range is calculated (X+Y)/2, so frequency range for the 180hz band is 125hz to 250hz. (180+70)=125 and (180+320)/2=250.
Adjusting the 180hz band will affect all sounds within its frequency range. Many instruments might have parts of their sounds here; You might want to adjust the bass instrument but end up affecting the drums and the guitars as well. This is the way EQs work, and while a more detailed EQ might somewhat remedy the problem, you need to go back to mixing to affect individual instruments (unless you made the track yourself or work in a big, famous studio, its unlikly you have access to the mix though).
We use Decibel to measure sound loudness. Decibel is
Logarithmic unit. To quote wiki "A change in power ratio by a factor of two is approximately a 3 dB change". That means +3 dB will make your sound twice as loud. Keep that in mind when you EQ.
To know what instruments are in what bands/frequencies, LFF recommended a carnegie chart. This can be a good idea, but experience will be far more helpful to pinpoint sounds. Metal vocals will not in the same frequencies as rap vocals. To get a better grasp of "where" the sounds are, play with your EQ. Set bands to max or min and observe how the sound changes. While not especially pleasureable, it will make you learn.
Aggressive EQing can introduce clipping in your music. You can avoid this by , as LFF said, "It is better to subtract, rather than add". Play with your EQ to learn what settings that introduce distortion, clipping and other artifacts.
If you see a switch/button/whatever and dont know what it does; click/switch/manipulate it. Its the best way to learn and unless you are working with live sound you cant break anything.
EQing is very simple but to get the wanted results might be very hard (unless you are EQing for fun/to learn, you should have a specific goal with your EQing. Like "compensate K701s lack of bass" or "make the cymbals not give me headache").
The day you find your EQ lacking, get a compressor.