Question about mults

[Alex_c]

Can anyone chime in on this? If anyone with an electronics background can answer this that would be great.

Cheers!

[Bill@WelcomeHome]

Originally Posted by Alex_c

Looking at wiring up a mult in my patch bay to split mic and line level signals so I can do some fair and somewhat scientific comparisons of different outboard pres and compressors. I am somewhat confident that the output impedance of the line level devices should be low enough, and the input impedance of my fireface should be high enough to split with the only side effect being signal loss, but what about i/o impedance from the mics to preamps? ... I have read some audio literature explicitly condemning splitting signals with a Y cable when feeding say, a power amp from a mixer.......

You can successfully split line level signals, less so mic level. But still, when you directly connect devices using a hard wired connection, they can interact with each other. And all a mult is, is a fancy wye, in that the devices are still hard-wire connected to each other.

But just to go to your original goal...what are you trying to compare that hasn't been compared thousands of times, by people using much more scientific setups (and knowledge) than yours? I'm not trying to be offensive, I'm saying that if you look around, the info may already be available. And if you split using either active electronics or a transformer, you've invalidated any attempt to compare as you've introduced elements that would not normally be a part of the signal.

This site: osCommerce has a lot of good comparisons.

side issue: it is very common for PA companies to wye the outputs of their crossovers to feed multiple amp racks.

[recordinghopkins]

Originally Posted by Bill@WelcomeHome

But just to go to your original goal...what are you trying to compare that hasn't been compared thousands of times, by people using much more scientific setups (and knowledge) than yours?

Ummm....

Maybe he wants to hear things with his own ears in his own place through his own gear? I know you gave the disclaimer that you're not trying to be offensive, but this is kind of presumptuous. He's not looking for comparisons by others, he wants to do his own.

Give the guy some more credit.

[Bill@WelcomeHome]

Originally Posted by recordinghopkins

Ummm....

Maybe he wants to hear things with his own ears in his own place through his own gear? I know you gave the disclaimer that you're not trying to be offensive, but this is kind of presumptuous. He's not looking for comparisons by others, he wants to do his own.

Give the guy some more credit.

The point to aiming at more scientific tests was that test performed incorrectly yield incorrect results and faulty conclusions. Given the questions in the OP, it is clear that the basics are not known by the OP, let alone the details that would render results invalid. There is too much to know or learn, starting from scratch. It is like wanting to build a guitar, and buying a spoke shave... it is a long road to get to a good guitar. If the goal is to learn how to do these things properly and go off into the tech world, great. But if the goal is to make better recordings, it might be more time and cost effective to search out the info and move on rather than learn how to distill it correctly and properly at home. But to each his own...

[recordinghopkins]

It sounds to me like he is doing his research and knows the basics, and is just looking for some clarification on impedance interaction. There isn't ever too much to learn when learning is your mission!

A "y" split with no transformers or resistor network will make both of the chains equal, but when you disconnect it and go back to only one chain it may slightly change the way the mic interacts with X preamp. Two matched transformers will have the same effect, but properly load the inputs. A passive split with only one transformer will skew the comparison.

The most accurate approach would be to set up a loudspeaker or monitor in front of the mic, play a pre-recorded file, then swap the preamp and do it again. If all you're looking for is to be able to do quick shootouts between preamps on say, a vocalist, then a passive Y is probably the best approach. Be aware that p48 may not behave with vintage gear connected in this fashion. There's not much to worry about with modern preamps. Passive non-isolated mic level splits are used all the time in live sound (although it's admittedly not the best way to go for FOH/Monitor splits). In your lab, the cable length is comparatively short so signal loss won't be a huge issue.

[tINY]

I'd suggest a different approach.

Use a recorded track and output it to some device (monitor speaker, guitar amp, furby...). Then you can play the track twice with the mic and source in the same positions and only change the cable connection to the pre-amp.

With mic at 200-300 ohms and pre-amps at 1k-2k ohms, the loading from another preamp is significant - transformer or wye split. While this is done in live situations, the differences aren't that significant with all the other issues that come with a full PA. And, the musicians do need to hear themselves...




-tINY

[Alex_c]

Originally Posted by tINY

I'd suggest a different approach.

Use a recorded track and output it to some device (monitor speaker, guitar amp, furby...). Then you can play the track twice with the mic and source in the same positions and only change the cable connection to the pre-amp.

With mic at 200-300 ohms and pre-amps at 1k-2k ohms, the loading from another preamp is significant - transformer or wye split. While this is done in live situations, the differences aren't that significant with all the other issues that come with a full PA. And, the musicians do need to hear themselves...




-tINY

Thanks, I have actually considered just using pre-recorded material but since the response of the speaker would colour the sound, I wanted to keep it as simple and "pure" as possible. I suppose I could try this on different source materials (vocals, guitar, drums etc) and see how the preamp responds to the different tonal characteristics of each instrument, with the speaker being the common denominator/detractor if you will.

Let me clarify on my previous statement where I said that splitting a signal with a wye is not a good idea, I mis-quoted the article I read and what is actually correct is that summing with a wye is a bad idea, which is what happens sometimes (in a pinch) in the live world, even though it should generally be avoided no matter what. Excuse my mistake, If I were a perfect audio engineer, I wouldn't need to post on internet forums!

[tINY]

The problem with not using a recorded source for these comparisons is that, at worst, you'll have different performances with the mic in different places (which could create more differences than the preamp). At best, you'd have one performance with two ('identical') different mics in slightly different positions. Matched pairs of mics will help.

You really can't run the mic to two pre-amps at once and expect normal performance from the gear.

If you are simply doing live tests - then just switch back and forth a few times and then do it again in a couple of days. It's less scientific, but you can get a good feel for the differences over time. Just remember that it's easy to fool yourself when the differences are subtle.




-tINY

[Alex_c]

Here's the explanation for the method used for the mic pre CD:
http://www.3daudioinc.com/3daudio_pretech.html

Looks like they used different performances for each comparison. Doesn't seem very scientific at all to me...

Here's a thread discussing the very product you mentioned:

Mic Pre's...3d Audio CD. is it crap? - Avid Audio Forums

Doesn't seem all that endearing. There's little to gain when we let our ego supersede our desire to learn.

I'm not trying to be offensive, I'm saying that if you look around, the info may already be available

Perhaps instead of assuming I "don't understand the basics", you could explain in detail the most scientific way of comparing mic preamps. Perhaps what you would do, should you ever want to make a comparison of your equipment, in your room, with your system.

I deal a lot with pompous people in this industry, and to be totally honest, I have worked with some very well regarded live and studio engineers. None of them have this attitude, and will always encourage someone to try things for themselves and experiment to see what works the best for them in whatever unique situation they are in. In fact, there is a mutual respect between us, as we all have our strengths and weaknesses in such a broad and multifaceted industry. If we recognize them as such, we can all learn from each other, regardless of experience or reputation, resulting in better relationships, better business, and most importantly, better recordings.

[Alex_c]

Originally Posted by tINY

The problem with not using a recorded source for these comparisons is that, at worst, you'll have different performances with the mic in different places (which could create more differences than the preamp). At best, you'd have one performance with two ('identical') different mics in slightly different positions. Matched pairs of mics will help.

You really can't run the mic to two pre-amps at once and expect normal performance from the gear.

If you are simply doing live tests - then just switch back and forth a few times and then do it again in a couple of days. It's less scientific, but you can get a good feel for the differences over time. Just remember that it's easy to fool yourself when the differences are subtle.




-tINY

Absolutely, which is why I was asking about the viability of splits. The performance is really the most important part of the whole signal chain, so to test different performances defeats the purpose of trying to find out which gear gets in the way the least.

Again, using two mics at once is something I never understood when people are doing shootouts. Positioning a mic a couple inches left, right, up or down can have a huge impact on what it sounds like. If I had a nickel for every time rolling a mic a couple degrees off axis, or moving an inch or two in a given direction gave me the sound I was looking for...well I wouldn't have enough to buy the 1073 I am lusting over, but you get the point.

[tINY]

And that is where playing with different mics on different sources and even in different rooms has value. Proximity effect? Off-axis coloration?

In a lot of ways, these shoot-outs only really highlight gross differences between mics. And then, if you did it again in a small, dead booth or a good live room you might choose a different one...

There were standardized tests for telephone systems using "lip ring" speaker horns. But that was a very specific test for intelligibility studies....

...art or science...




-tINY