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what's the purpose of a summing mixer
Old 3rd July 2018
  #151
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Quote:
Originally Posted by Matt Syson View Post
Hi

[As far as i understand, the whole point of an op amp is that it keeps the voltage at the mixing point (right after the resistors) at a constant voltage, basically presenting each resistor input with a high impedance, thus preventing the individual channels from interacting.]

Sadly incorrect. In a 'Virtual earth' summing system the summing point is 'effectively' ground (hence the name virtual earth). In theory these will be no measurable VOLTAGE at this summing point, it acts like a short to 'earth'.
However it is current summing so a signal voltage through the summing resistor puts a current into this point and as the amplifier is assumed to have infinite gain it's output rises (or falls) depending on the polarity of the current and through the negative feedback resistor 'nulls' the incoming CURRENT (basic op amp theory saying that the 2 inputs must be the same voltage for the output to be zero).
No, i'm afraid you've got it backwards. It's the voltage that gets canceled out. This is how the 'virtual ground' is created!
Voltages cancel out, so you have the same voltage as at the positive input (so not necessarily ground, could be any arbitrary voltage in range).
And there will be a current flowing through the feedback resistor and back to the mixing resistors that supplies every input with what they need at that time. So the current perfectly follows the sum of the inputs. That's why it is such a great setup!!
It basically turns the 'naive' resistor mixer into something more perfect.

If you only have resistors then some of one resistors energy will flow back through the other inputs resistors. And that makes it non-linear (thus technically, less ideal) summing. This problem is removed by the op amp.
Old 3rd July 2018
  #152
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Well I am glad you are so confident you are correct.
Working on mixers for 42 years for 5 manufacturers and they ALL got it wrong?
Another name for 'virtual earth' summing is current summing.


[As far as i understand, the whole point of an op amp is that it keeps the voltage at the mixing point (right after the resistors) at a constant voltage, basically presenting each resistor input with a high impedance]
No it is a LOW impedance not high. It's called Virtual earth, not virtual infinity.

Matt S
Old 3rd July 2018
  #153
Quote:
Originally Posted by Audiofool View Post
Quote:
Originally Posted by croger View Post
I was considering a summing mixer until I looked inside a Dangerous 2 buss LT. bunch of chips and wire.... on a small PCB board.
Not so much chips and cables but a lot of LEGO.

This is obviously an over priced box. Simple summing network with some relays (“LEGOs”) for panning and cheap IC amps for make up. That also doesn’t mean it can’t have a nice impact on the sound, or that it’s “snake oil.”

But yeah, there is a pretty major difference between this and something like The Oracle or the CAPI “sumbus” which are way better, and a far better value for what you’re getting.

Last edited by psycho_monkey; 4th July 2018 at 01:16 AM..
Old 3rd July 2018
  #154
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Quote:
Originally Posted by chinesewhiteman View Post

This is obviously an over priced box. Simple summing network with some relays (“LEGOs”) for panning and cheap IC amps for make up. That also doesn’t mean it can’t have a nice impact on the sound, or that it’s “snake oil.”

But yeah, there is a pretty major difference between this and something like The Oracle or the CAPI “sumbus” which are way better, and a far better value for what you’re getting.
The Oracle is what I am talking about. It is something I would use. bravo. Bravo. I need to look at that piece of gear.

Last edited by psycho_monkey; 4th July 2018 at 01:17 AM..
Old 4th July 2018
  #155
Quote:
Originally Posted by croger View Post

The Oracle is what I am talking about. It is something I would use. bravo. Bravo. I need to look at that piece of gear.
YEAH! I've been using the DIYRE SB2, which is the simplest and cheapest little summing box out there. It's only $50. It's totally passive. The mixer it self is probably not doing all that much, or contributing anything important to the sound(I wouldn't argue on that point one way or the other), but you use amps of your choice as make up gain because it's passive and with that it can have "a sound" and you can make it exactly what you want.

I also have 6 channels(and counting) of DIYRE Colour modules. There are a bunch of really good sounding subtle, and not so subtle, saturation "Colours" and other effects as well. I'm still dialing in what exactly I want my "mini console" to be, but that's the fun and the power...you can taylor it to you. Now, I think what most of us are really after when we're looking to analog mixing is "vibe" and "mojo"... something that will have a euphonic effect and it's no wonder that we scoff at a boring "pile resistors and wire" and rightly so especially considering that should cost but a few bucks. Now, IMO the best Colours for this purpose hands down, are Louder Than Liftoff's "Royal Blue" and Mass Driver." Respectively, Neve and API console channel circuitry in miniaturized form. I'm thinking I'll load up my channels with a combo of those. Of coarse you can just get a pair and swap circuits and reamp tracks till the cows come home, but I just like breaking everything out at once and listening and adjusting in real time, hence why I like to use a mixer.

I am really considering the CAPI sumbus too.

Last edited by psycho_monkey; 4th July 2018 at 04:53 AM..
Old 4th July 2018
  #156
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The dangerous 2 buss plus has colour options now. They say it adds character. Seems they are following the wants of the consumer.

Yes. For summing I want it to sound different. Mojo, color, tubes and transformers, etc.. I want it to be easier to get "the" sound that's in my head. So imo the 2 buss LT is a waste. The original 2 buss as well. Since they said it's the exact same circuit as the LT model.

Quote:
Originally Posted by chinesewhiteman View Post

YEAH! I've been using the DIYRE SB2, which is the simplest and cheapest little summing box out there. It's only $50. It's totally passive. The mixer it self is probably not doing all that much, or contributing anything important to the sound(I wouldn't argue on that point one way or the other), but you use amps of your choice as make up gain because it's passive and with that it can have "a sound" and you can make it exactly what you want.

I also have 6 channels(and counting) of DIYRE Colour modules. There are a bunch of really good sounding subtle, and not so subtle, saturation "Colours" and other effects as well. I'm still dialing in what exactly I want my "mini console" to be, but that's the fun and the power...you can taylor it to you. Now, I think what most of us are really after when we're looking to analog mixing is "vibe" and "mojo"... something that will have a euphonic effect and it's no wonder that we scoff at a boring "pile resistors and wire" and rightly so especially considering that should cost but a few bucks. Now, IMO the best Colours for this purpose hands down, are Louder Than Liftoff's "Royal Blue" and Mass Driver." Respectively, Neve and API console channel circuitry in miniaturized form. I'm thinking I'll load up my channels with a combo of those. Of coarse you can just get a pair and swap circuits and reamp tracks till the cows come home, but I just like breaking everything out at once and listening and adjusting in real time, hence why I like to use a mixer.

I am really considering the CAPI sumbus too.

Last edited by psycho_monkey; 4th July 2018 at 04:53 AM..
Old 4th July 2018
  #157
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Old 4th July 2018
  #158
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Quote:
Originally Posted by Matt Syson View Post
Well I am glad you are so confident you are correct.
Working on mixers for 42 years for 5 manufacturers and they ALL got it wrong?
Another name for 'virtual earth' summing is current summing.
Yes, but you stated that the current was 'nulled'.
This is not happening. The current through the feedback resistor is the sum of the currents through the resistors.
The voltage is what gets canceled and thus the virtual ground is created.

Quote:
[As far as i understand, the whole point of an op amp is that it keeps the voltage at the mixing point (right after the resistors) at a constant voltage, basically presenting each resistor input with a high impedance]
No it is a LOW impedance not high. It's called Virtual earth, not virtual infinity.

Matt S
Yeah, you're right, i was confused. It's low impedance.
Old 4th July 2018
  #159
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The current IS nulled as at the summing point the only significant currents are those through the input resistor and from the feedback resistor. No current flows into the op amp. Basic op amp theory.
Matt S
Old 4th July 2018
  #160
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Quote:
Originally Posted by Matt Syson View Post
The current IS nulled as at the summing point the only significant currents are those through the input resistor and from the feedback resistor. No current flows into the op amp. Basic op amp theory.
Matt S
I wouldn't say that current is nulled. For an ideal op-amp, there's two equivalent ways of describing the situation. We can look at it as current summing: the inverting input has infinite impedance, and so the only current path is through the feedback resistor to the load. This current drops a voltage across the feedback resistor, which appears at the output. Since the direction of the current (for a positive input) is from feedback resistor to output, the resulting output voltage is the negative of the summed input voltages.

Or we can look at it in terms of op-amp action. With a negative feedback path, the op-amp will do anything it can to make its two inputs have a common voltage. Since the non-inverting input sees 0 V, and the inverting input sees some voltage V+ (the sum of the input voltages), the op-amp output must provide a voltage V- across the feedback resistor to bring the inverting input to 0 V. This is the voltage null that I think monomer is describing.

Both analyses are equivalent, so I don't think you guys are actually disagreeing.
Old 4th July 2018
  #161
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Quote:
Originally Posted by Matt Syson View Post
The current IS nulled as at the summing point the only significant currents are those through the input resistor and from the feedback resistor. No current flows into the op amp. Basic op amp theory.
Matt S
But i never claimed this!
Of course no current flows through the op amp.
Old 4th July 2018
  #162
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Quote:
Originally Posted by bogosort View Post
Both analyses are equivalent, so I don't think you guys are actually disagreeing.
Agreed!
I think we both made imperfect descriptions from different viewpoints.
I tripped over the statement that current gets nulled.
But on the other hand i was talking nonsense as well by stating inappropriately a high impedance for the mix point.,

I'm still convinced that having the op amp involved is better then passive, but i find it hard to motivate..
It seems obvious that with a good op amp the passive version will be noisier, but what i'm really worried about is the channels loading each other in the passive version. But i'm not sure how that works out in practice. Probably has a lot to do with the impedances of the arriving signals.
Old 4th July 2018
  #163
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Quote:
Originally Posted by monomer View Post
I'm still convinced that having the op amp involved is better then passive, but i find it hard to motivate..
It seems obvious that with a good op amp the passive version will be noisier, but what i'm really worried about is the channels loading each other in the passive version. But i'm not sure how that works out in practice. Probably has a lot to do with the impedances of the arriving signals.
I don't think the passive will necessarily be noisier, but the virtual ground provided by an op-amp definitely helps isolate the inputs. Passives also have the problem of varying bus impedance, which changes as channels are switched in and out.
Old 4th July 2018
  #164
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Quote:
Originally Posted by bogosort View Post
I don't think the passive will necessarily be noisier, but the virtual ground provided by an op-amp definitely helps isolate the inputs. Passives also have the problem of varying bus impedance, which changes as channels are switched in and out.
Thank for claring that up.
Old 5th July 2018
  #165
Quote:
Originally Posted by Gutz View Post
Summing porn
Old 5th July 2018
  #166
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As usual in many cases there are advantages and disadvantages.
Depending on the 'external' factors either voltage or current summing (current being the virtual earth case) one can appear 'better' than the other.
Virtual earth has many advantages in that if few channels are connected (they must be switched completely off) then a sum of a handful of channels will have very low 'noise'. VE summing 'suffers' from noise due to the gain which increases as more input resistors are added.
Thus summing 2 channels the noise can be very low, -110dBu sort of territory. If you have around 30 channels 'selected' then the noise will go up, IIRC around 25dB or more. Of course this is not actually terrible but it suggests that for QUIET mixes you should 'unroute' (disconnect completely) all channels you don't need. This is NOT what happens if you 'mute' a channel on most mixing desks.
In contrast a 'passive' summing system usually has it's summing bus level around -30dB and it's 'makeup' amplifier will have this related amount of noise happening all the time, irrespective of the number of channels selected. From this you can start to see that for a summing system of say 30 channels the resultant unwanted noise can be about the same. These numbers are indicative of the trends, not 'worked examples'.
There are also other factors like changing frequency responses and so on that all influence the decisions.
Matt S
Old 5th July 2018
  #167
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I'm glad we've got past the "just a bunch of resistors" thing as passive summing is not what is used in LFACs, which is presumably what people want to emulate. The mix bus in a SSL 4K goes through 4 or 5 5534s and a VCA, so its not very surprising that it sounds different to an API where the mix passes through 3 DOAs ...

The CAPI summing kits should be ~£300 all in for 32ch of DOA summing loveliness, I'd build it with fixed input gain and a stepped attenuator for the mix out.
Old 5th July 2018
  #168
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Quote:
Originally Posted by Doc Mixwell View Post
Summing porn
Just my way of getting thread notifications, at 3200 bucks they look pretty sweet though
Old 5th July 2018
  #169
Quote:
Originally Posted by Gutz View Post
Just my way of getting thread notifications, at 3200 bucks they look pretty sweet though
The Heritage MCM mixers are totally sweet.
Old 6th July 2018
  #170
Quote:
Originally Posted by Gutz View Post
Just my way of getting thread notifications, at 3200 bucks they look pretty sweet though
The easier way is to click “subscribe” at the top of the post but yes very pretty!
Old 7th July 2018
  #171
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Quote:
Originally Posted by psycho_monkey View Post
The easier way is to click “subscribe” at the top of the post but yes very pretty!
This is gearslutz, a little porno seemed appropriate
Old 7th July 2018
  #172
Gear Head
 

I was very interested in a summing mixer, but decided to get a console instead. Couldn't pass on 32 channels of EQ. Seemed like a no-brainer! If you want a piece of analog sound in your mixes, you might as well grab some EQ's and faders too.
Old 8th July 2018
  #173
Quote:
Originally Posted by 88Keys444 View Post
I was very interested in a summing mixer, but decided to get a console instead. Couldn't pass on 32 channels of EQ. Seemed like a no-brainer! If you want a piece of analog sound in your mixes, you might as well grab some EQ's and faders too.
True, though it depends on workflow, recall needs, budget and if you do any tracking!
Old 8th July 2018
  #174
Gear Head
Quote:
Originally Posted by risingson8 View Post
what ever you say i love my neve 8816 it does something unique that none plugin able to do its not overhyped thing it does its thing basicly you just like it or not , just matter of taste.
I totally agree. My 8816 is the centerpiece of my studio. I would never part with it. Just makes everything sound so smooth. Like a nice butter glaze on top of my mix. Much better starting point than straight up ITb. And to me that is what it’s about. How close can I get to the finished product can I get without touching a single individual channel, and then making the few tweaks necessary. This thing def gets you on your way
Old 10th July 2018
  #175
Gear Head
 

Quote:
Originally Posted by psycho_monkey View Post
True, though it depends on workflow, recall needs, budget and if you do any tracking!
Agreed 100%. I was very worried about recall when I switched from ITB to getting a console. I used the faders to get a solid balance of the mix. With the EQs on the board, I do very broad amounts of EQ on tracks, especially in the high frequency range. Digital always gets that weird harsh sound, but my analog EQs don't. So then I basically have a decent mix with a good amount of EQ done. After that, I throw whatever coloring, reverb, delays and whatnot ITB. Makes recall much easier

Of course, to each his own. As long as the finished product sounds good
Old 3 weeks ago
  #176
Gear Head
Quote:
Originally Posted by SpookSound View Post
analog summing = very expensive way to improve a mix by 5%

...well, isn't the SB2 retailing at $50?...is that expensive?
Old 3 weeks ago
  #177
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Quote:
Originally Posted by McNewlove View Post
...well, isn't the SB2 retailing at $50?...is that expensive?
Indeed, filthy cheap. Built a slightly modded one with channels 3-6 mono up the middle, and using hand matched carbon resistors, because I am fruity like that. Works and sounds great.
Old 3 weeks ago
  #178
Gear Nut
My whole goal with buying a cranborne 500 adat was to get analog summing and saturation inside of something that I can use also to record. Just filling it with stereo pairs of preamps with independent saturation controls like RND silk or that camden mojo. I watched a few youtube videos where people were showing off the same mix summed in digital vs. using waves NLS vs. using a dangerous summing mixer and I felt like the analog summing was better. I have been throwing my money away ever since.

I don't feel guilty about it at all because while I build my summing mixer I am also building my front end. Someone on here recommended the id22 and I will be forever grateful, because I originally wanted to just pipe in a focusrite octopre box, but I saw those analog summing videos and also heard about the cranborne 500 adat all at the same time and like I said, I just started slowly shovelling the money into it. Eventually I will have something really unique, and being able to decide between 4 different kinds of saturation, (even more with the different mojo options and was thinking of going for something like a mono gama with the three options, but that might be a little pricey since the 511s already wrecked me more or less,) for every bus and switch it all up and just have options. Mmmm. Going to be sweet.

I'll report back in like... a year or so probably when I have it all together. Maybe less.
Old 3 weeks ago
  #179
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Hi
The limitations of 'simple summing' probably encourage more thought, creativity and effort into getting the sound you actually want, before attempts at 'correction' in the box. If the 'source' material is good, it makes life easier all round.
The difference in work flow simply adds to this rather than any 'technical' improvements as such.
Matt S
Old 2 weeks ago
  #180
Gear Head
Quote:
Originally Posted by chinesewhiteman View Post
I don't think he's saying that. He's just talking about a passive summing network, the point of which is to be transparent... but then come amps for make up gain, which are your first factor of character.

A lot of this really is about digital vs analog. Now when comparing x, y, or z mixer you're of course going to have differences because they'll all have different designs, circuits and components surrounding the summing. WE GET IT! If you strip "summing" down to JUST the summing portion of a given mixer...there is maybe a minuet difference OTB vs. ITB, but it's irrelevant as there is no real world means of stripping away all the components and that's never what we're actually talking about, nor trying to do when those of us who use analog mixers go OTB.

Even though it's subjective, let's say hypothetically the sonic differences are negligible between x and y...there are other factors/features/design etc. that each piece will have that will inform, or inspire you to work a certain way and make certain decisions when mixing. That's why you really have to get your hands on something in order to judge it. Plus everyone's perception and perspective is different so I can only put so much weight on what Joe Schmo says about x, or y, even if he has mixed dozens of platinum records.

Like I said before, just as with components and their implementation surrounding (it's summing network) being paramount in differentiating mixers; what you put/do before and after the mixer is what matters most. That's why I really like a simple passive summing box like the DIYRE SB2 because it allows you to customize exactly what that is going to be. And to me that's the idea of a summing mixer, whether it's something as stripped down as the SB2, or something like the Chandler mini mixer, you're tailoring what your setup is based on what is optimal for your own means and workflow.
Hi thanks, McNewlove here. I am very interested in the DIYRE SB2 but my head is swelling with confusion over it. My current front end set up consists of my microphone going straight into the preamp of my SPL Crimson 3. the Crimson of course has two mic pres. I am wondering, with this set up, can I add the SB2 or do I need extra gear? I read somewhere that I need two step-up mic pres and at least 8 monitor outputs? I believe the Crimson has only 2 monitor outputs?

could you please explain the set up requirements and procedure for the SB two and whether my current set-up can be used to leverage it?


its confusing because i read somewhere that all i need is mic pres and that the SB2 will allow me to impart the color of the mic pre. The Crimson has two discrete mic pres that i believe will serve me well in the mean time before i buy a dedicated pre, Godwilling sometime next year.

please do explain the set up process so i see if it is worth going down the SB2 route or looking elsewhere. Thanks
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