| Author | Message | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 3314 Registered: 6-2002 |
I'm just really checking my understanding of this so please correct any misunderstandings I may reveal in my post. I've read that the range of the Low Pass Filters on alembics is 350Hz to 6kHz so am i right in thnking that the filter only filters frequencies between those limits and anything outside that gets attenuated by 12db/octave? There is a long thread somewhere about why the limit is 6kHz at the top end as there is all kinds of noise up there and that makes complete sense. However I don't recall anything about what happens at the bottom end of the range. So my question is, what happens to frequencies below 350Hz. http://alembic.com/club/messages/16271/41122.html?1182027166 In that FAQ thread there is a line "When the control is rotated completely counterclockwise you get a flat response up to the filter setting." So does that mean you get a flat response on all frequencies below 350Hz including the sub bass frequencies or does it mean that it is flat only between the upper and lower filter range and beneath the lower filter point the signal is attenuated by 12db/octave as it does at the upper filter limit? Jazzyvee (Confused) | ||
| cozmik_cowboy
Senior Member Username: cozmik_cowboy Post Number: 1394 Registered: 10-2006 |
When the the filter knob is at one stop, the filter passes all freqs above 6K; at the other stop it passes everything above 350; in between, the cut-off varies as per the position of the knob. The quote after the link pertains, I believe, to the SII Constantly Variable Q knob. At counterclockwise (I think that's "anticlockwise" your side of the water, no?) response up to the freq at the given filter knob position has no boost; at full clockwise, there's a boost of (IIRC) 16dB at the filter freq, with 1-15.99999dB boost in between, depending on the position of the knob (for SI, that would be flat at position 1, with boosts at 2 & 3). Peter ps - Modders; why won't the alt-10-key codes work anymore? I used to be able to put an omega in for ohms) | ||
| mario_farufyno
Senior Member Username: mario_farufyno Post Number: 865 Registered: 9-2008 |
You can say that any signal's portion below filter's upper frequency limit should pass virtually unaffected trough a Low Pass Filter, although it is expected some ripple in the response near cut off frequency (some say that those glitches are what makes analog circuits so appealing). The Q switch can also add a ressonant peak on that limit, making Filter's "colour" even more evident (+12dB really is SOME ripple, isn't?). There is no limitation concerning lows on using magnectic coils Pick Ups (as low/high impedance changes affects its upper frequency response), so we could expect relatively flat response below LPF cutoff. But interaction between signal from PUs placed distant along the string can produce cancellations and reinforcements known as Comb Filtering, though. Depending on distance between PUs, their signal sum will eliminate a certain frequency (and its odd harmonics, too) affecting deeply our Bass tone. (Message edited by mario farufyno on February 06, 2013) | ||
| mario_farufyno
Senior Member Username: mario_farufyno Post Number: 866 Registered: 9-2008 |
As you may know, tone is a result of the Harmonic Series generated when we pluck a string. The string motion is complex and happens simultaneously in various modes. Each of these shapes (vibrational mode) produces a simple tone that are spaced and ordered in harmonic way (in multiples of whole numbers). So if an A string oscilates in 55Hz (cicles per second), in its fundamental mode (1st Harmonic), it will also sound in 110Hz (55 x 2) in the second harmonic, 165Hz (55 x 3) in the third and so on. This is the so called Harmonic Serie. All that simultaneous movements and its corresponding frequency combine in a particular resultant that characterizes Tone. There are always some non-harmonic partials also going on, and the change on tone during time known as envelope, but important to us is that this harmonic modes creates knots (no movement) and bells (full move) along the string. As lower is the overtone, less divided the string will be and more towards center its focal point will get (right in the bell's middle). As upper is the harmonic, more divided the string will be, and we will get some focal point all along entires string. So it is easier to sense those upper modes near the Bridge and that is why that bridge PU sounds brighter (because it'll get a weak movement of lower harmonics while sensing some upper harmonic right in on spot). This means each different PUs generates diverse signal content and, probably, out of phase in some frequencies related to the other. When mixed these 2 signals can interact and change each other as the sum causes that spaced holes in the spectrum described as the spikes of a comb that rids off alternated harmonics, which obviously transforms tone entirely - independently where the cutoff frequency is. This is only mixing PUs dependant and has nothing to do with Filter's operation. It really doesn't change your tone below Filter's cutoff frequency, but this combinated signal isn't exatcly flat at all, though... (Message edited by mario farufyno on February 06, 2013) | ||
| mario_farufyno
Senior Member Username: mario_farufyno Post Number: 867 Registered: 9-2008 |
They claim turning full clockwise being flat because it rises cutoff frequency towards 6KHz. As the PU can't reproduce signals above this, naturally falling -12dB per octave above that, there is no loss in limiting upper spectrum in 6KHz. Any coil can induce electricity flow under changing magnectic field. This can be provided by metal string bouncing near and far from PU magnet surrounded by a conductive coil. That is the principle of a magnectic PickUp. But as they also have a increasing resistance while frequencies gets higher in an effect known as Inductive Reactance (a part of total Impedance of a circuit), coils ends being natural filters to high frequency signal, since they passes lows easy but resist to highs. Bigger is the coil, greater is that Reactance. In fact, most PUs can't even reach that high since focus more on improving signal's strenght at expenses of narrowing the spectra. They opt using heavy coils to acomplish this, since very winded coils can produce bigger magnectic fields and stronger electric signals. On Alembics they seem to made the oposite choice, sacrificing volume in favour to the idea of getting a wider frequency response PU, using light coils (low impedance PU) to get it. This is clearly why they had to install a preamp right after the PUs, to raise its weak (but broad) signal before sending it trough a long cord. The fitering capabilities are a plus benefit on having an onboard preamp and Wickersham's ingenuity raised it to a state-of-art. * If you want to sound more like conventional or traditional basses, cut Filter off lower (conter-clockwise). Alembic can mimic the limited response of traditional PU systems at some extent... (Message edited by mario farufyno on February 06, 2013) | ||
| terryc
Senior Member Username: terryc Post Number: 2057 Registered: 11-2004 |
way too technical..use your ears!!!! | ||
| 811952
Senior Member Username: 811952 Post Number: 2268 Registered: 10-2003 |
It's a low-pass filter. Everything below whatever frequency the filter is set to, within reason, passes. John | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 3319 Registered: 6-2002 |
I've read this a few times and I think I'm ok now with what is going on. I understand that whatever is below the frequency gets passed as I just wanted to know if any processing is done to the frequencies below the lower cut off to make them flat up to the 350Hz when the filtering cuts in. I have been told many times that there are a lot of clear sub frequencies in the sound of my basses at least now I can be clearer in my explanation of how things work. Yeah Terry it is technical however if i'm on stage doing some knob twiddling at least I know why I'm doing it and hopefully I can explain what I was trying to achieve when I'm finished. hahaha Jazzyvee | ||
| terryc
Senior Member Username: terryc Post Number: 2058 Registered: 11-2004 |
jazzyvee..took me six months to master the controls and get the sounds I want..now I can select P bass thump, j bass mid range honk to clanky ricky! I hadn't a clue how they worked just used my well wornout ears! | ||
| afrobeat_fool
Senior Member Username: afrobeat_fool Post Number: 504 Registered: 7-2009 |
Don't feel too bad, bro. I have just started to understand the SF-2! I found the SII electronics were easier, due to having a SI for a few years. You jumped in the DEEP end with a quickness. I wonder witch Alembic line of electronics you will end up liking the most? | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 3322 Registered: 6-2002 |
Although it took me ages to grasp, and I think I posted equally frustrating threads, I have found the signature setup and my sc deluxe easiest to work with so far and I can find the sound I want pretty easily. The addition of the 3 position q switches and strings recommended by PierreYves the bass sounds like its been given an overdose of whatever the bass equivalent of eucalyptus is. That said, I can with the series 2, see the benefit of two volumes even though its slower for me to find the sound I want. Having played single volume guitars for ever moving to two is not instinctive to me yet. One of the area's I find tricky on the series II is deciding if the sound i'm seeking would be achieved by adjusting the q or volume for one or more pickups. I guess like Terry suggests its just about using my ears and in addition to that, knowing what you expect the sound to do before you turn a control so you know you are going to be heading to the sound you want rather than blindly searching for that elusive tone by trial and error which could be distracting and just get you to the wrong sound for the song. I've actually only gigged twice with his bass and those were very short sets and thats mainly because if I were to use it on one of my jazz-funk gigs I'd need to set radically different tone changes to give me sounds similar to Marcus, victor bailey, jimmy haslip and Stanley Clarke before I started playing and be close enough to fine tune during the song. I know I can't do that yet. I haven't yet found my home tone position like I have on my sc bass and its very much a work in progress. All that said, I think it's a fantastic sounding instrument and I'm really pleased I decided to own it. Once I get the hang of it all will be fine. Jazzyvee | ||
| flpete1uw
Intermediate Member Username: flpete1uw Post Number: 152 Registered: 11-2011 |
Jazzy, I just picked up a Series 1 and yes there is a Major learning curve. I too have always used a master volume which the Series 1 lacks. I toyed with the idea of a volume pedal but nixed the idea because I want to learn this Gal on her terms. The best advice I heard was playing each pickup separately to learn the nuances than combine them. I'm finally at a point where I have a starting point or should I say a fallback position. Then I slowly experiment from there. I agree the Q switches add or subtract in ways that seam unintuitive. But in time I'm sure it will all may some sense. Best of Luck in the exploration Pete | ||
| nnek
Member Username: nnek Post Number: 83 Registered: 8-2009 |
I just got my series I electronics restored by the mothership and I thought I knew how my bass worked but now I see how limited the range was on it before the repairs! With a nod to Pete, I could only get one pickup to work reliably for quite a while before all signal finally failed forcing me to send the guts back to Mica. Now I find myself relearning a bass I've had for many years. The Q switches and selector switch as well as several components of the board were replaced. Now I'm having a hard time just trying to get the old sound I was using for the bridge pickup. It's just like a whole new world opened up within an old friend... Kenn | ||
| dfung60
Senior Member Username: dfung60 Post Number: 577 Registered: 5-2002 |
Jazzy - Series EQ controls are a little more complicated, but it's fairly easy to visualize. On your garden variety bass, the tone knob is a simple passive low-pass filter. Beyond a certain frequency (the corner frequency), any higher freqs are attenuated or filtered off. When you turn the knob down, you lower that corner frequency and more and more of your output signal is getting filtered off. The corner frequency and how it changes is based on the relationship between the capacitor in your control cavity and the resistance value of the potentiometer. In the tone control, the pot is wired so the resistance increases as you turn the knob down. This is the simplest low-pass filter you can make (called and RC filter, because it's just a resistor and capacitor). When it cuts frequencies, it does so pretty gently. Any time you put a capacitor across the signal lines, you create an RC filter. A long guitar cable can have considerable capacitance, which is why you might lose highs with a long cable in a passive setup (you won't hear this, but your guitar player will). The Alembic EQ is a more advanced kind of filter. With the the Q-switch in the "up" position, the EQ pretty much acts like a traditional low-pass filter. There's an active preamp in the circuit, which takes the cable capacitance out of the picture, and the starting corner freq of the EQ is also a little higher than a Fender. But it pretty much acts like a regular tone control. In the other two positions of the Q-switch, Alembic is playing an interesting trick. This control is tweaking the frequency response of the preamp so that there's a sharp peak in the gain right at the resonant frequency. Below the corner frequency that you're picking with the knob, the sound is unaffected. Above the corner, it's being cut like the regular tone control. But right in the vicinity of the corner frequency there's a big boost happening. This size and shape of resonance can't easily be reproduced by passive circuits, so positions 2 and 3 of the Q-switch are something special. Position 2 (middle) creates a small resonant boost and Pos 3 makes a large one. Turning the tone knob is now both boosting and cutting frequencies. You can sweep the peak through both the harmonics and high fundamentals of the bass and create a lot of sounds that wouldn't otherwise be possible. I like to tune my bridge pickup to get more pick snap in pos 3, but would normally run the neck pickup in pos 1. You may notice that if you select Pos 3 on the Q and turn the filter knob while repeatedly plucking the string, it almost sounds like a wah-wah pedal. This is very similar to what a wah pedal is doing - moving a resonant peak through the freqs. Most wah pedals are set up as a different kind of filter (bandpass) which creates a resonant peak and cuts everything above and below the center frequency. Although you can simulate the Series resonant peak with a wah, it would probably wipe out your low end. In a Series II, the circuit is the same, but now you can adjust the height and sharpness of the resonant peak with the CVQ knob. So, the best way to approach the Series EQ is to think of Pos 1 as a "regular" tone control. To tune in some extra snap, you can use Pos 2 and 3. The switch setting will control the amount of snap, and the knob will let you tune where the boost is happening. David Fung | ||
| cozmik_cowboy
Senior Member Username: cozmik_cowboy Post Number: 1396 Registered: 10-2006 |
"...it pretty much acts like a regular tone control." Unless I'm completely misunderstanding this, I'll have to disagree and say they work in pretty much opposite fashion. The traditional tone knob works, for want of better imagery, vertically; the freq is set, and the knob controls the rate of roll-off. The Alembic filters work horizontally; the roll-off rate is fixed, and the knob controls the cut-off frequency. No? Peter | ||
| edwin
Senior Member Username: edwin Post Number: 1415 Registered: 5-2002 |
Peter is right, the knob that the Series basses have is a frequency knob while a traditional tone knob is an amplitude knob. I don't know if I would use the word opposite as the results can be similar in some settings, but in terms of the axes of frequency vs. amplitude, that's correct. Also, I would posit that Alembic and many other pickups are quite capable of capturing frequencies above 6khz. It's just that there is no useful information that comes off a bass string above 6khz. The highest note on a 6 string bass will usually be C5 which is 523.25 Hz. Which means the next overtone of that will be roughly 1.05khz, the next above that is 2.1khz, etc., so 6khz is high enough about the fundamental to allow for a significantly bright tone to be heard. For lower notes, where you would more likely be utilizing the brightness of the notes in snapping and popping, 6khz becomes much higher on the harmonic series for a given note. Keep in mind that octaves double when the frequency doubles to you're really within a couple octaves of the limit of hearing (one octave up to 12khz, which is probably the limit or close to it for us old folks who have been beating up our ears for decades and then an octave above that is 24khz, which no one really hears). | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 5346 Registered: 7-2004 |
Edwin: You understand math too well for a lawyer! hehehehe I think what David was attempting to say was that the Alembic LP filter is similar to a standard passive tone pot in that clockwise gets you more treble and counter-clockwise gets you less treble. Perhaps overly simplistic, but essentially accurate. Bill, tgo | ||
| edwin
Senior Member Username: edwin Post Number: 1419 Registered: 5-2002 |
Hey, don't be callin' me names, I ain't no lawyer yet! But, yes, that's true in terms of more treble and less treble, which is why I wasn't into using the word opposite as the results of an Alembic LPF and a standard Fender style tone control can be similar. It's also why I prefer my pan pots the reverse of most people. Clockwise should be be more treble! But, I also don't think I was being pedantic in emphasizing the difference as we are a pretty discerning bunch and thus can hear the difference between amplitude and frequency adjustment. The main point I was trying to make was that despite the fact that there is always a constant filter on the high frequencies, it is flat for our purposes when the filter is completely clockwise. This post really lays it out like it is: http://alembic.com/club/messages/393/19319.html?1119689541#post40850 | ||
| cozmik_cowboy
Senior Member Username: cozmik_cowboy Post Number: 1397 Registered: 10-2006 |
Thanks, Edwin; Frequency v. Amplitude states it more clearly than my "opposite", which I came up with visualizing it as a graph with frequency as the X axis & amplitude as the Y. Peter | ||
| mario_farufyno
Senior Member Username: mario_farufyno Post Number: 874 Registered: 9-2008 |
Great link, Edwin! Note the comb filtering I was talking about... | ||
| gtrguy
Senior Member Username: gtrguy Post Number: 577 Registered: 9-2004 |
Wow! I just turn the knobs till I like the sound, then I turn the knobs on the amp and have to start all over. | ||
| edwin
Senior Member Username: edwin Post Number: 1423 Registered: 5-2002 |
Yeah, the amp vs. bass controls is definitely something to get under control. It's made even more complicated by the fact that the bass control adjustments definitely go to the PA while the amp adjustments may or may not depending on where the PA gets the signal. My philosophy is to use the amp controls to get a good basic sound in the room and then use the bass to adjust the tones for each musically appropriate section. That part does often involve turning the knobs until I like the sound! | ||
| that_sustain
Intermediate Member Username: that_sustain Post Number: 108 Registered: 8-2012 |
I've recorded twice now with my bass. From these experiences I've found the filtering switches are basically an easily controlled limiter/compressor for your sound. Would this be correct? | ||
| sonicus
Senior Member Username: sonicus Post Number: 2793 Registered: 5-2009 |
Not correct. Filters do not do what a compressor or limiter do . A filter attenuates frequencies. A limiter or compressor attenuates amplitude /gain . | ||
| edwin
Senior Member Username: edwin Post Number: 1424 Registered: 5-2002 |
Not really. A limiter or compressor keeps the signal from going over a specified threshold. In other words, they deal with the dynamics (loudness or softness) of the sound. Equalizers deal strictly with frequency response. While the two can seem to be related, a properly designed equalizer, such as the Alembic filters are, should not affect the dynamic range of the signal. | ||
| that_sustain
Intermediate Member Username: that_sustain Post Number: 109 Registered: 8-2012 |
lol I don't get it. All's I know is it's great. I notice the bass sounds burpiest with the treble switch flicked downward, Q switch flicked forward...and the tone knob rolled on a little less than halfway. | ||
| that_sustain
Intermediate Member Username: that_sustain Post Number: 110 Registered: 8-2012 |
...oh, and with both pickups on, also. I get a "Walk This Way" sorta tone with these settings. Thanks Alembic. | ||
| edwin
Senior Member Username: edwin Post Number: 1425 Registered: 5-2002 |
Well, you don't have to get it to enjoy it and make sounds that others will love. Clearly you really do get it because you know how to do that! | ||
| gtrguy
Senior Member Username: gtrguy Post Number: 581 Registered: 9-2004 |
Oh yeah, the "Walk this Way" Fender phase honk thing. I knew a guy back in the day who was a fan of that and managed to mess with his bass till it sounded like Aerosmith. Compression can pump the quiter parts of the signal and also squish the top, with speed and amount and sustain variables (and a little bit of noise), like a super fast many fingered person on the sound board sliders. A limiter I think usually refers to a virtual hard top of the slider preset type position that the signal level can't go over. Is this a good analogy? | ||
| edwin
Senior Member Username: edwin Post Number: 1427 Registered: 5-2002 |
That's a pretty good analogy. Technically, compression is measured in a ratio, such as 2:1, where 1 db comes out for every 2db the signal goes over the threshold. For low ratios, you have compression, such as the above, where 10db over the threshold would still give you 5 db out. Higher ratio compressors become limiters. Usually over 10:1 is considered the beginning of limiting. There is brick wall limiting, which is essentially infinity:1. The speed of the attack and/or release is also a consideration, where compression can have quite slow attack and or release (and in fact, slow release is pretty much a necessity for bass compression because if it's too fast, it interprets the actual wave as individual notes and can result in distortion) whereas limiting tends to be very fast attack and release. Having a slow attack can allow the articulation of the note through at the beginning, but then bring down the level. This can accentuate the attack of the note. Having a fast attack can clamp down on the initial impulse of the note (often the loudest part when measured) and then with makeup gain, the sustain can then be made louder, giving the sense of a smoother tone. So, compressors are very powerful and can create quite a range of sounds. Noise is not a necessary artifact of compression. My Grace M103 (preamp of choice these days) has a compressor that is capable of quite a bit of compression and adds no noise whatsoever. Where compressors gain (pun intended) the reputation for being noisy is that after you've compressed the signal, often you add gain on the output which brings up the noise that was in the signal before the compression. Limiters can also create this consequence. So, at the end of the day, they are related. Both are useful for bass, depending on your sonic goals. (Message edited by edwin on February 18, 2013) | ||
| growlypants
Junior Username: growlypants Post Number: 33 Registered: 3-2011 |
Fantastic explanations! I'm going to school, big time! Thanks so much for these truly enlightening discussions! | ||
| that_sustain
Intermediate Member Username: that_sustain Post Number: 111 Registered: 8-2012 |
Yes, much appreciated. |
