what’s the difference?
what do the names mean?
what other filter types are there, someone said something about cheaper diode 12db filters that could be used on a cheaper moog synth what are these?
I know that 12db, 24db refers to the slope that the freqencies are cutoff by
and i know the different types of filter like LPF, HPF, BPF and notch (are there any others)?
the main thing i want to know is how are the filters made and how the design changes the sound, MOOG sued ARP for stealing their filter design on the original odyssey II, so ARP had to design their own four-pole LPF
the design must be important for MOOG to sue ARP, i just want to know a bit more about them.
Without getting too technical here, a state variable filter is an active filter (as opposed to passive) that can provide multiple filter response types (LPF, HPF, BPF and band-reject, or notch filter) simulateously. As a result, state variable filters are popular filter designs for synths.
The term ‘ladder filter’ refers to Bob Moog’s patented design of a LPF based on pairs of transistors that schematically have the appearance of a ladder. I don’t think Bob’s design is a state variable filter, but MC can certainly clarify the details here.
Other than the four filter types you mentioned, there’s also an all-pass filter that is used to shift the phase of a signal. In addition to analog designs, there are also digital implementations of filters that can easily exceed the response characteristics of any analog filter.
Filters can be designed with either active or passive components. A simple tone control, like the ones found on a stereo receiver for example, can be designed from just a single resistor and capacitor. This ‘design’ results in a -6 dB/octave filter (AKA 1 pole) - a very low cost way of adding some filtering. The type of filter (either active or passive), the design, selection of components and even the way the filter is constructed will collectively affect the ‘sound’ of the filter.
The reason Moog sued ARP was because ARP infringed on Moog’s patent. Moog’s original patent has since expired and now anyone can use that design, AFAIK.
I was wondering why Synthesizers.com was getting away with their transistor ladder LPF module…I guess it’s because of the patent expiration you metioned…thanks! that was making me very confused for awhile now…
Speaking of the schematic of Bob’s transistor ladder…I was thinking of getting it tattooed on my arm…then filling in the circular part of one of the transistors with the Moog logo…cool eh?
Maybe Moog would sponsor my arm…like all those people you hear about in the news using their body art for advertisement…
I guess since i’m an EE it’s ok to have nerdy tattoos right?
A tattoo is an expression of who you are so I don’t think that would be nerdy, just more intelligent and thought out than a clown or a naked woman with flames. Nick got the Moog logo and he’s proud of it so I say go for it. I have 2 tats myself and I just made sure I wanted them on me for the rest of my life and that they meant something more to me than a fad.
As far as selling the advertising space, don’t they usually do that on the forehead. That may be a little extreme plus that seems like a place where a tattoo would hurt like the dickens. The needle might actually hit your skull. OUCH!
The patent granted for the Moog LPF was issued on October 28, 1969. You could Google it to get the details. It’s patent # 3,475,623, called “Electronic high pass and low pass filters employing the base to emitter diode resistance of bi-polar transistors”.
Interestingly, the filter is the only item from Bob’s original synth designs from the 1960’s that was patented.
The big difference between state variable and Bob’s ladder filter is that the latter can be voltage controlled.
Before the ladder filter, voltage controlled filters didn’t exist. Varying the cutoff frequency of a filter with a control voltage was a problem because you needed to vary the R element of the RC product of a filter. Optoresistors was one solution but had a very limited bandwidth. Other solutions did not provide a natural linear response or had limited control range.
The ladder filter was the first workable solution to a voltage controlled filter, and its approach was unique enough that it was rightly awarded a patent. Bob recognized that by varying the emitter current in a transistor, the emitter resistance could be varied over a wide range/bandwidth and was linear over that range. He exploited that feature to use the emitter resistance to form the variable R component of the RC product of the filter.
I have a Synthesizers.com synth, which is very fun. I have both the State Variable filter, and the Ladder filter. Both are decent filters… nothing jaw-dropping, but nice. The one thing I can say is, however, the ladder filter does NOT sound Moog-like. Doesn’t sound anything like any of the Moogs I have or have had. (Minimoog, Micromoog, Sonic Six, Moogerfooger Lowpass, and Opus III)
As an overall answer. The circuit design of a filter has a great impact on the character of the sound. Even if 2 filters claim to be doing the same thing - i.e. 24db low pass - they can sound very different. On top of that a filters behavior when feedback is applied can sound vastly different.
Woldn’t that make sense if they were trying to copy the Low Pass Filter in the modular. It is a different design after all. I know MOTM and the Alesis A6 also went for the 904 design. Also the strength of the signal is a key factor. It’s desirable to overdrive the filter somewhat. Doing so won’t turn a differen’t filter into something that sounds like a particular Moog but it will have an impact on the character of the sound as does the VCA design and it’s being slightly overdriven.
One thing I’ve noticed is that while about half the active modular makers have some sort of filter based on some sort of Moog (I was talking to a latterday builder once and some people will reject buying a whole new system if there is no Moog filter in it) I’ve not seen any copies of the Modular High Pass filter. The only place I see something High Pass and Moog is the new already coupled design in the Voyager. (For what it’s worth you can make a band pass and notch from a high and low pass pair)
And also the little differences of the matched transitors of the top and lowest ladder pair change the sound. The Voyager uses way better matching tranistors (actually a transistor array (very much like also used on the Waldorf Pulse) where the original Moog filters of the mudular and Minimoog used early transistors that there not that perfect matched then todays transistors or transistor arrays.
Q:
Didn’t the Oberheim SEM modules used a state variable filter? I think so.
And it was of cause voltage controlled.
Perhaps, but it would seem to me that if you market a filter as being a “ladder filter,” you’re drawing a parallel. The Moog ladder filter was a patented design for years, and is known for its ladder design. If you’re just making a filter that slightly overdrives the signal, you might as well call it a “filter,” without making reference to the circuit design that so specifically references another filter, with a very distinctive sound.
I’m satisfied with my dot com (God, wouldn’t Arrick have been a better synth brand name???) ladder filter as a filter, but it lacks a distinctive quality that would make it stand out as a specially-labelled filter. When I bought it, I saw reference to it as being regarded as the same as having a Moog filter in your modern modular. Which it is not. : ) But, again… it does what a filter should, and I’m keeping it. : )
what if all of the transistors in the ladder are matched?- not just the top and bottom? Would it sound better? I’ve been told it’s not done for cost reasons, but would it be worth it in a custom filter?
The Waldorf Pulse uses two CA3046 transistor arrays (5 transistors each)
see here some pictures a friend of mine did while I opened his Pulse: http://faq.waldorfian.info/pulse-inside.html
The Moog Voyager filter transistors are constructed from the CA3086 transistor array. I am not sure about details, because there is no service manual or schematic available for non Moog-techs
The Moog Source, the Rogue and the Prodigy uses a CA3046 transistor array for the matched filters at the top and the lowest ladder step.
I think a filter with all matched pairs or all transistors matched will loose some of the roughness of the sound when being overdriven slightly.
Yeah but my RAM Minimoog (#1053) with all matched transistor pairs in the ladder has a resonant quality that doesn’t exist in later models where only the top/bottom pairs are matched. I’ve had mine and later Minis side-by-side (even with same VCO board) and the difference was night and day.
I’ve heard two other RAMs (#1001 and #1009), both with different VCO cards from mine, and they sounded identical to mine.
So RAM Minimoogs (and Musonics) will be consistent from one model to the next., while later Minimoogs with only the top/bottom pairs matched will vary from each other. There were also changes to the mixer resistors during production which will change the sound.
Which is why lots of folks claim that the Voyager doesn’t sound “like their minimoog”. FWIW, my Voyager sounds very close to my RAM Minimoog.
True, but you can’t get a notch (AKA band reject) response from the Voyager’s filters. The configuration doesn’t allow it. This is too bad, as a notch filter could be used to generate some interesting new timbres.
What’s really a shame is that the Voyager’s high pass filter can’t be accessed separate from the low pass (both are in series and summed to the left and right outputs). A high pass filter by itself (and with resonance, please!) would make for some REALLY interesting sounds.
Could prob. be done in the software right? I mean the hardware components are already installed. Maybe they will add these filter features in the future if enough people demand them.
Points well taken about the effect of transistor matching in Minis.
My point about cloning was even more basic. The modular filter has similarities (certainly when it comes to patent coverage) but is not the same filter design as what is in the Mini (or the Micromoog or the later instruments).
“The Q150 Transistor Ladder Filter is based on Bob Moog’s famous design and provides incredible-sounding -24dB lowpass filtering which has become the standard of subtractive analog synthesis.”
Of course a person could, with intention, read that and assume that they are NOT suggesting that the filter sounds like the Moog filter they plainly state it is based upon… but I think it takes a little effort. ; )
And, if that quote isn’t enough, there is a quote on the page that says:
“MR Wrote: As a former Moog System 55 owner, I can say that the Q150 filter is as good as a 904a filter to my ears… it really is. and again before anyone wants to start a flame war… I put them side by side… and actually Rogers was a bit “cleaner” too… so dare I say, almost better.”
Honestly, I can’t imagine how the filter I have could be considered “better” than a Moog filter.. ANY Moog filter… but perhaps I got a lame dot com filter, or perhaps MR had a lame System 55 filter, I don’t know.
What I do know is that it looks like Arrick is portraying this filter as sounding Moogish. : )
