Xorg dependency graph (BLFS)

I'm in the process of building (again…) a Linux From Scratch system (and writing some scripts to automate the process a bit).
My base system (LFS proper) is done, and now I'm in the BLFS part. After a couple of basic packages, I need to tackle Xorg.
The dependency graph is quite big, following the dependencies by hand is tedious and error-prone. To ease the task, I decided to make a couple of graphs with Graphviz (in the DOT language).

Here's the result (and you can find the dot files here or here).

Just some notes:

• to keep the graph manageable, I didn't include any "optional" dependency (but I put some in comments in the dot files)
• one graph has "required" and "recommended" deps, the other one only "required" (plus the run-time deps)
• solid lines are "required"
• dash lines are "recommended"
• grey lines with dot heads are "required at run-time"
• for wget, I put as "recommended" "gnutls or openssl" - because I think it makes sense - but I didn't expand them (gnutls in particular would make a mess in the graph). I already installed wget before looking into Xorg, anyway, and I assume that everybody else would do the same
• in the dot files, I explicitly set [style=solid] for the "required" deps, so it's easy to change them with sed if desired
• with graphviz installed, generating the images from the dot files is as easy as: dot -Tpng xorg_depgraph.dot >xorg_depgraph.png 
• the blue-ish (ghostwhite) nodes are the ones outside the chapter 24 of the BLFS book

EDIT 2015-09-21: added some colouring, fixed gist link
EDIT 2015-09-22: added glib dependencie
EDIT 2015-10-13: checked against BLFS 7.8 (and fixed titles), fixed xorg-server

How to cross-strap your bass or your guitar with 2 regular straps

I have a couple of heavy bass guitars which really hurt my left shoulder after a while, so I looked for a way to balance the weight between both shoulders.
I tried some commercial cross straps but the best solution I found is just using 2 regular straps (I saw Michael Manring using it).

Here's how:

• use one strap just as usual
• with your guitar on, attach the second strap to the tail pin (I have Straplocks on the bass shown in the photos, so I put the second strap underneath the first one; if you don't have Straplocks it's easier to put it on top)
• this second strap needs to be adjusted longer than usual
• pass the second strap over your belly, than around your left flank and across your back to reach over your right shoulder (I'm assuming you're right-handed)
• attach the second strap to the horn pin

Some notes:

• the instrument stays in the "usual" position, just like with a single strap (unlike some harnesses i tried, which kept my bass in an awkward position)
• it's easy to adjust the strap to the right length
• it's stable and keeps your instrument in place, but at the same time you can adjust the position without even fiddling with the strap length
• on some pins it's hard to fit two straps: you may need to find straps with thin ends, or longer pins
• it seems awkward at first, but after a bit of practice, you can learn to put the strap on without even detach it (hint: you need to "rotate" it over the horn pin, I'm sorry but I don't know how to show this with a photo)

Les Paul mods: "treble bleed"

 Hi folks. Another post about Les Paul circuitry customization: this time I'll show the effect on the tone of the so-called "treble bleed", a mod that many people consider a good enhancement.
The rationale for this mod is that when you turn down the volume, you hear what many consider a loss of treble. Looking at the graph it seems that this description is inaccurate, because as you turn the volume knob, initially the resonant peak get smoothed (and here there is actually some treble loss), but then the frequency response extends a bit, with a resonant peak that is less pronounced but higher in frequency than the one at full volume. So I think the ear just get just "tricked" a bit. Or maybe the real-world components just behave different enough from the ideal ones of these simulations to arise the bad volume behavior.
Whatever the truth, the "cure" is to add a small capacitor between the pickup pin and the middle pin of the volume potentiometer to let some treble "bleed" straight to the output. Many people advocate to add a resistor in series or parallel.
The problem is that the values of the capacitor and the resistor and their configuration are pretty critical. In general the bigger the cap the more dramatic the effect, while the resistor smooths somewhat the effect.

I chose here to show a parallel configuration, with values matching ones from this forum thread. It seems, looking at the plots, to be a nice combo, with a distinct but not overkill effect on the sound.
The graphs shown are logarithmic plots of the frequency response from 20 Hz to 20 kHz between the pickup ideal signal and the output, for the standard wiring and for the one with the treble bleed, and for different positions of the volume potentiometer (I set ten values of a logarithmic sweep from 1 Ohm to 500 kOhm). The first plot is for the tone knob fully on bright (on "10"), and the second one is for the tone knob fully on dark (on "0").

 

You can clearly see the effect: with the tone on bright and partial volume, the resonant peak is lower in frequency (and, with this cap value, in a position close to the one at full volume) but more pronounced, and, with both of the tone positions, the roll-off of the high frequencies is less steep, as expected, giving a brighter tone.

Note, however, that there's no effect at full volume, where the steeper roll-off is retained; this implies a more or less pronounced timbre change as you turn the volume knob.

The effect of the volume knob is also a bit slower near the full volume and faster near the lower end.

For a more in-depth analysis, you can check this excellent thread.

Of course, this is just a circuit simulation with ideal components; if you want to know how this translates in reality just open your axe, check some different caps and resistors, and - as always - let your ears be the judge!

PS:

The software I used for the simulation is Qucs on Linux, but on the website you can find downloads for Windows and Mac OS X as well.
There's no potentiometer component in Qucs, so I just used two resistors with the values bound together by the equation Rvb=500k-Rva.
For the pickup I chose values that, combining various sources, seem to be good representatives of a standard Gibson PAF pickup.

Les Paul mods: "independent volumes" wiring

Another post about Les Paul circuitry customization: this time I'll show the difference between the standard "modern" wiring and an alternate wiring I found here with "independent volume controls". The rationale about this mod is that with the standard wiring, when you set the 3-way switch on the middle position, if you turn fully down the volume of one pickup, you silence the signal of both. But how do this mod affect the controls behavior?

I'll analyze here the circuit with only one pickup, i.e. with the 3-way switch NOT in the middle position. The graph shown is a logarithmic plot of the frequency response between the pickup ideal signal and the output, for the two wirings, and for different positions of the volume potentiometer (I set ten values of a logarithmic sweep between 1 Ohm and 500 kOhm). The tone knob if fully on the bright position

 

As you can see, with the alternate wiring, as soon as you turn the volume knob down the sound gets very very dark! My bet is that this is not what you want, but if you want to try this mod anyway, go ahead and let your ears be the judge (I didn't, I just ran the simulation).

My opinion is that the volume silencing both pickups is a non-issue, actually, because if you need to silence just one pickup, why selecting both, anyway? You could just flip the 3-way switch and you're done.


PS:

The software I used for the simulation is Qucs on Linux, but on the website you can find downloads for Windows and Mac OS X as well. There's no potentiometer component in Qucs, so I just used two resistors with the values bound together by the equation Rvb=500k-Rva. For the pickup I chose values that, combining various sources, seem to be good representatives of a standard Gibson PAF pickup.

Les Paul mods: 500kOhm vs 250kOhm volume potentiometer

Another post about Les Paul circuitry customization: this time I'll show the effect on the tone of substituting the volume potentiometer with a 250kOhm one (the standard being 500kOhm).
The graph shown is a logarithmic plot of the frequency response from 20Hz to 20kHz between the pickup ideal signal and the output, for the two choices of volume potentiometer, and for different positions of the volume knob (I set ten values of a logarithmic sweep from 1Ohm to 500kOhm).

As you can see the effect of the 250k volume pot is to smooth the resonant peak, making the sound a bit duller.
The effect becomes less and less significant the more you turn the tone knob towards the dark position, so here I show the results only for the brightest position.
(Btw, using a 250kOhm potentiometer for the tone knob would just be like keeping the stock 500kOhm one turned down a bit. Not interesting at all.)
Of course, this is a circuit simulation whit ideal components; if you want to know how this translates in reality just open your axe, check some different pots, and - as always - let your ears be the judge!
PS: The software I used for the simulation is Qucs on Linux, but on the website you can find downloads for Windows and Mac Os X as well.
There's no potentiometer component in Qucs, so I just used two resistors with the values bond together by the equation Rvb=500k-Rva.
For the pickup I chose values that, looking at various sources, seem to be good representatives of a standard Gibson PAF pickup.

Les Paul mods: 47nF vs 22nF vs 15nF tone capacitor

Hi folks. If you own a guitar, you are probably aware that there are a bunch of customizations that you can do with the passive circuitry of your favorite axe.
There are lots of websites that shows and explain different mods, but it's hard to find one that shows some data or nice graphs. So, inspired by this forum thread, I did simulations for some Les Paul mods (I own an Epiphone Les Paul Custom) and I'll post some results.
This one shows the effect of changing the value of the tone capacitor. Popular choices are 47nF, 22nF (these are the ones I found in my guitar) and 15nF.
They usually say that smaller caps give brighter tone, but how exactly do they affect you sound? Here I'll show you.
The graph is a logarithmic plot of the frequency response from 20Hz to 20kHz between the pickup ideal signal and the output, for the three values of the capacitor, and for different positions of the tone potentiometer (I set ten values of a logarithmic sweep from 1Ohm to 500kOhm).

As you can see, the different capacitor values are non-influential when the tone knob if fully on the bright setting ("10" position), but the more you close the tone, the more the effect of the capacitor becomes apparent: with lower cap values, the resonant peak for the dark tone position shifts higher in frequency and becomes more pronounced.
This holds true at whatever volume position: these plots are for full volume setting, but I could have chosen another volume position as well.
So the bottom line is: smaller caps give brighter sound, but only when the tone knob is on a dark setting. In other words, a smaller cap limits how dark the tone can be. This can translate in being able to use the full range of the tone control without the sound getting "muddy".
Looking at some forums, it seems that many people like a 15nF for the neck PU and a 22nF for the bridge one.

Of course, this is a circuit simulation whit ideal components; if you want to know how this translates in reality just open your axe, check some different caps, and - as always - let your ears be the judge!

PS:
The software I used for the simulation is Qucs on Linux, but on the website you can find downloads for Windows and Mac OS X as well.
There's no potentiometer component in Qucs, so I just used two resistors with the values bond together by the equation Rvb=500k-Rva.
For the pickup I chose values that, combining various sources, seem to be good representatives of a standard Gibson PAF pickup.