there is no "PURE" way to A/B compare, but what about active splits?

[didier.brest]

Please note that the first four posts in this thread were moved from another thread.
The positive posts were removed to help continue knowledge and practice with regard to this topic.
I trust we can keep this thread moving in the right direction.

Originally Posted by supoUSA

there is no "PURE" way to A/B compare - Y's will not work purely and neither will splitters.

Why an active splitter would not work 'purely' ? It might change a bit the input signal from the microphone but if well designed shoul do it the same at two indirect outputs.

[supoUSA]

The active mic splitter won't work because the mic signal is applied to an amplifier circuit. This circuit is actually a mic preamplifier.

The output of this mic-pre is fed to several more amplifiers which feed the various split outputs required.

Additional circuitry in the mix invalidates the purity. Best way to do the test is same mics, same cable plugged into unit 1, then unplugged and put in unit 2. The only problem is because this is a live performance, you won't hear the same material. But, everything else stays the same.

[didier.brest]

In my previous post (closed thread), I gave a link to an active splitter with 0 dB gain. Why the electronics inside is is an issue ? There is also electronics in a condenser mic. My point is that at an active splitter output, the signal has a mic level and the impedance seen by the preamp is also similar to a mic impedance. So for the preamp, the pair microphone + splitter is equivalent to a microphone, not the microphone that is an element of this pair but we do not care about that since we are interested in comparing two preamps, not in evaluating a particular microphone.

[supoUSA]

Originally Posted by didier.brest

In my previous post (closed thread), I gave a link to an active splitter with 0 dB gain. Why the electronics inside is is an issue ? There is also electronics in a condenser mic. My point is that at an active splitter output, the signal has a mic level and the impedance seen by the preamp is also similar to a mic impedance. So for the preamp, the pair microphone + splitter is equivalent to a microphone, not the microphone that is an element of this pair but we do not care about that since we are interested in comparing two preamps, not in evaluating a particular microphone.

Mic to recorder = pure. Mic to splitter to recorder = not pure. The way I'm not doing it is the purest way.

[NorseHorse]

Doesn't anyone own matched mics? I certainly consider matched mics suitable enough to compare preamps, and I have done so on several occasions.

And to test A/D, just use the same source material, whatever that is. For instance, record prerecorded material instead of a live performance. It could be played via Line level, a speaker source, or even an instrument like an organ or piano with memory.

If you're still stressin', you should probably have a glass of wine. Splitters aren't needed for tests.

[ghellquist]

Y-cables definitely is a viable alternative. It has the advantage of giving both inputs exactly the same circumstances, recording exactly the same electrical signal.

Given a modern design condensor mic the signal will not be effected in any serious degree by the halving of load impedance. I would not use it with unamplified ribbon mics though, but things like the Royer SF24 is not a problem.

And if you wonder, yes I´ve done it quite a few times. Only with "professional level"equipment though, for low-priced plastic boxes you need to look more closely at the design.

// Gunnar

[aussie_techie]

using different microphones means that you are hearing a different micing position, not much of an issue for distance micing but for close micing it can be, having another mic in the way can also interfere with the pickup pattern. it also comes down to how accurately matched your mics are.

that said a pair of DPAs always seems to be small enough to position and matched closely enough for this to work.

[John Willett]

There is a very simple way to do a "pure" comparison between two recorders.

You just need a matched pair of omni microphones - put them together in the same place and send one to one recorder and the other to the other recorder with identical cables - record.

Then - swap the mics over and record again.

That way you can do a proper comparison between the two machines and the swap will remove any differences due to any tiny differences between the matched mics.

Simple and easy.

[JEGG]

Originally Posted by John Willett

You just need a matched pair of omni microphones - put them together in the same place and send one to one recorder and the other to the other recorder with identical cables - record.

Then - swap the mics over and record again.

That way you can do a proper comparison between the two machines and the swap will remove any differences due to any tiny differences between the matched mics.

It may be tiredness, but I don't quite follow this. Will this reveal anything about imaging (I understand this to be an inherently mono test-2 mic's in the same place), and does this require two identical live performances (an impossibility) since an inter-channel swap is necessary, or are we recording electronically generated sounds?

The likelihood is that I'm misunderstanding something.

Onward:

To the point of how to do comparisons of recorders: it seems to me that this discussion over several threads is both overly complex and yet misses the "larger picture" entirely.

One could record some relatively complex wide bandwidth source-an orchestra, perhaps, in a decent acoustic space. During the session, the same pair of mic's (omnis, perhaps 0.75 m spaced, and power hungry ones could be helpful) could simply be "rotated" among the various machines under comparison. The test would definitely not involve identical performances, in fact, it wouldn't even require that all of the excerpts be of the same portions of pieces, nor would it be necessary to have the same pieces recorded.

However, with only three or so machines under test, it is likely that a significant portion of the recorded material would be the same repertoire selection, but not the same performance.

With this method, more of each of the machines are involved-for example, we get the results of each machines phantom power supply.

I think a great deal could be gleaned from a few (or a few more) 30 second recordings from the gear under consideration. I wouldn't have any difficulty drawing conclusions from such a simple test.

It has something else going for it as well-it's definitely the easiest and the least time consuming, and may have the best chance of actually being done.

[BrianHanke]

The fundamental issue with all comparisons like this is that there are multiple complex variables at play. Therefore, isolating *just* the recorder (or preamp, or converter, or whatever) is quite difficult.

Elsewhere on this forum I saw someone propose what I thought was an excellent solution: record numerous takes using the exact same microphones in the exact same place, swapping recorders for each take. Once you have 20 takes from each recorder listen back and see if you can identify trends in the sound.

If, while listening blind, you can correctly identify which of the 40 clips were made with which recorder you'll be well on your way to understanding the sonic fingerprints of the devices in question.

This approach has the benefit of not needing any special equipment, nor does it require a completely controlled experimental environment (something most of us do not have access to).

[John Willett]

Originally Posted by JEGG

It may be tiredness, but I don't quite follow this. Will this reveal anything about imaging (I understand this to be an inherently mono test-2 mic's in the same place), and does this require two identical live performances (an impossibility) since an inter-channel swap is necessary, or are we recording electronically generated sounds?

The test I suggested would show up the differences in the mic., pres. and the quality of the two machines.

If you want to do a stereo recording for imaging you would have to record in stereo with one machine and the swap machines (without changing anything else) and record the same piece again - the only difference would be the performance, but would show imaging differences as the mics and musicians would not have moved.

[Martin Kantola]

Have suggested (for pre-amp testing) a special microphone with dual outputs. Practically speaking it's two sets of output circuitry in the microphone itself. Think I know how to build this now, and best case will finally have some time to get it done pretty soon.

Martin

[JEGG]

Originally Posted by John Willett

The test I suggested would show up the differences in the mic., pres. and the quality of the two machines.

If you want to do a stereo recording for imaging you would have to record in stereo with one machine and the swap machines (without changing anything else) and record the same piece again - the only difference would be the performance, but would show imaging differences as the mics and musicians would not have moved.

I guess I did understand it (previous post). I think the simple swap machine procedure-recording different performances or even different material-would be telling enough to form general impressions.

That is-if it were ever done! I'm hoping it will be.

At this point, though, perhaps we should all give the whole thing a rest until someone has the opportunity and time to do something.

[Plush]

I fail to understand--- what might be wrong with splitting the mic signals through traditional splitters?

Using these splitters (all the same brand/model) each microphone would be "affected" in the same way. ( I don't believe there is much if any degradation with high quality splitters.)

The reason that the splitters make sense to me is that they allow the same program material to be sent to a number of machines and they allow each machine to use its own mic amps and its own converters. This provides a true picture of each manufacturer's "recording system."

I would specify passive splitters with Jensen transformers as a good starting point.
These are used every day in high quality audio pursuits.

[MichaelPatrick]

Originally Posted by Plush

...what might be wrong with splitting the mic signals through traditional splitters? ...

I would specify passive splitters with Jensen transformers as a good starting point.
These are used every day in high quality audio pursuits.

[didier.brest]

It was also my initial proposal but there was an objection in the closed thread about such a passive splitter not isolating the input from the outputs regarding the impedance. So I understand that the rendering from a mic at splitter input and a preamp at splitter output A would depend of the preamp A impedance and the impedance (vs. frequency) of the preamp at ouput B. This objection does not hold for an active splitter. Looks like the absolute arm for preamp shoot-out. I think that what is proposing Martin is putting the active splitter in the mic.

[Plush]

The transformer isolates the input of the recorder from the mic. Same transformers all around present the same "look" to each recorder's mic inputs.
This is yet one more way to level the playing field.

I don't buy the objections to the splits. They are a red herring.

[Remoteness]

I agree with Plush here.

I would use a three way splitter with one direct out and two transformer isolated outs.
The direct out would go to a preamp that will only power the mic(s).
The two isolated outputs would be connected to the two different recorders.
This will indeed (as Plush so eloquently said) "present the same "look" to each recorder's mic inputs. This is yet one more way to level the playing field."

Originally Posted by Plush

The transformer isolates the input of the recorder from the mic. Same transformers all around present the same "look" to each recorder's mic inputs.
This is yet one more way to level the playing field.

I don't buy the objections to the splits. They are a red herring.

[Audiop]

Using splitter makes no sense to me.

The mic sees another load than it does feeding the preamps directly. The transformer adds some distortion and bandpass and not necessarily the same to both pres.

You can not test the phantom supplies since only one can feed the mic.

Such a test might as well be substituted with a attenuated line level feed which is perfectly fine for testing a preamp.

What you will not get a grip on with a line feed is the +48V supply and how the mic interacts with the input impedance. The latter is not really a preamp issue though but a microphone issue.

I have done and propose the following:
Record a loop with a DA-AD. Insert a preamp in loop and run the same signal again.

You can run this test with different gain settings and different material. If you can not hear a difference with the preamp in the loop it means it's transparent for this listener in this test set up which is a good thing in my book. I have tested the Line Audio 8MP this way and could hear no signature from the preamp in the loop.

Once you have a clean preamp circuit you can go on and test the +48V but if a preamp can not pass a loop test without detection it does not matter (to me) how stable the 48V supply is.

Even if transparency is not your goal the test described above makes sense anyway since it's the only way to learn about the colorations that the preamp (or any other transmission link) may have.


/Peter

[didier.brest]

Originally Posted by Plush

The transformer isolates the input of the recorder from the mic.

No it does not. The mic sees the impedance of the preamp through the transformer:

2005 AES Convention paper

[Remoteness]

Originally Posted by didier.brest

No it does not. The mic sees the impedance of the preamp through the transformer:

2005 AES Convention paper

Yes, the mic does see the impedance of the preamp through the transformer, but it's still isolated chassis to chassis.

[Plush]

Originally Posted by didier.brest

No it does not. The mic sees the impedance of the preamp through the transformer:

2005 AES Convention paper

In practice I see nothing wrong with that. The mic also sees the impedance of the preamp when it is plugged in to the recorder. What is the difference? The difference in impedance will not change the sound perceptively. These are all excuses to not get a comparison done.

I find that objections to splitters to be splitting hairs. The transformers involved don't change the sound that much. The mic input impedance in most modern recorders is very high and as such is unlikely to affect the sound quality.

Each person objecting to splitters has helped lead another poster down a dead end path.

The goal is to actually be able to compare the equipment. And I mean compare mic amps and a/d converters on the two machines. Sending line level signals leaves out the mic amp design.

I have compared many machines and have always used splits and always the same program material. Have I been doing it wrong?

[Suda Badri]

Null test in order I think.... one file mic straight into a recorder, one file with a splitter in the way... flip phase.... what happens.... infinite null?

I should try this anyway... will post results if I do it tonight...

[didier.brest]

Yes, the mic does see the impedance of the preamp through the transformer, but it's still isolated chassis to chassis.

Yes. So because the mic sees the impedances both from preamp A and preamp B, it does not perform on any of them like it would if it was linked directly to it only. And one cannot say that the performance loss is equivalent for both preamps. So the comparative test might be claimed being unvalid by some people here who like to be critical about everything. I agree that this claim would be likely excessive and I would be much interested in a preamp shoot-out even with a passive splitter.

I find that objections to splitters to be splitting hairs. The transformers involved don't change the sound that much. The mic input impedance in most modern recorders is very high and as such is unlikely to affect the sound quality.

The AES paper just states the contrary. You have to submit your own paper to the next AES convention.

[Plush]

Purely theoretical, Didier. NOt seen as an objection in practice. YOu're guessing what would happen, aren't you?

Whenever I have done tests with this method, I've gotten real results that I can use and make judgements with. They have been valuable.

[didier.brest]

I don't know whether the impact of the mic seing the impedances of both preamp is significant or not. I did not write any paper to AES.

I know that the comparative listening between two preamps may be much demanding when two quality units are on the ring. Hence if one can avoid some possibly unfair factor, doing so is certainly better .

[panatrope]

There are many points in our audio pursuits where comparisons (elsewhere deemed odious) are necessary, sometimes as an aid to where to spend our hard-earned savings, sometimes to prove that our choice is superior, sometimes in a quest for greater understanding and sometimes to track down faulty behaviour.

Like the old carpenter's dictum of "measure twice, cut once", the most critical part is working out your test methodology and ensuring that it will deliver the focus on the behaviour of the object(s) under test that you wish to consider; get someone independent and like-minded to comment in a disinterested manner in what you propose to do; then do it precisely according to your test plan and document everything in the process.

In designing a test, it is generally regarded that most effective comparison process will occur where you only change one thing at a time and everything else remains identical. The greatest challenge is the live test material. I liked the approach of Reference Recordings when they wanted to do Direct to Digital, a modern day implementation of the Majorca/Sax direct to disc efforts of the '70s. For their musical subject, they chose pianist Dick Hyman performing some classic ragtime, which he recorded by performing on a high-class Disklavier (using 16-bit - MIDI, that is). Then for the recording sessions, they could play back the MIDI and the performance would be exactly the same each time. When they had the levels right, they pressed the 'Record' button, knowing that the performance would be exactly the same as the rehearsal.

So can I suggest that you search out someone who has a good performance space and a Disklavier. That means that for a comparison, you can change precisely one element at a time (microphone, preamp, recorder) and subject it to the same source material, for as many tests as you like. There will be some debate for instance when testing microphones, where they have different sensitivities, whether changing the gain of the preamp is a sufficient change to invalidate the 'change only one thing at a time" paradigm. I will leave the rest of you Obsessive-Compulsives to debate that one - this O-C has already made his contribution.

Comparisons are interesting ... but disciplined rigourous testing is rare but wonderful. (Hugh Ford, where are you when you are most needed?)

[Audiop]

Originally Posted by Plush

In practice I see nothing wrong with that. The mic also sees the impedance of the preamp when it is plugged in to the recorder. What is the difference?

The difference is that the mic (possibly) sees another impedance in the primary of the transformer and that the two secondary windings may give different results with the two preamps and also as comapred to the mic driving the pre's directly.

The difference in impedance will not change the sound perceptively.

What kind of tests or analyzis made you come to that conclusion?

These are all excuses to not get a comparison done.

No, it's about making sure the test does not give false results. If so all energy put into
the test would be for nothing. Do it right or don't do it at all.

I find that objections to splitters to be splitting hairs. The transformers involved don't change the sound that much.

But "not much" is to much. A good pre doesn't change the sound that much either.. or possibly not at all.

The mic input impedance in most modern recorders is very high and as such is unlikely to affect the sound quality.

That wold depend on the source impedance.

Each person objecting to splitters has helped lead another poster down a dead end path.

Absolutely not. Just bringing the attention to the problems with such a test.
Are you suggesting that everyone should agree on everything? I think the discussions would not be discussions anymore in such case and I don't understand your negative attitude.. this time either.

The goal is to actually be able to compare the equipment. And I mean compare mic amps and a/d converters on the two machines. Sending line level signals leaves out the mic amp design.

Wrong. The input circuitry only sees a voltage and an impedance. It does not matter if this voltage comes from a mic or an attenuated line level stage. Heck even some mic's has line level outputs.

An attenuated line level signal is perfectly fine for investigating any coloration from the mic amp.

I have compared many machines and have always used splits and always the same program material. Have I been doing it wrong?

Possibly and I guess that's why you are so negative against the idea of that method having problems.

How big these problems are needs to be investigated in every specific situation.


/Peter

[John Willett]

Originally Posted by Plush

The transformer isolates the input of the recorder from the mic. Same transformers all around present the same "look" to each recorder's mic inputs.
This is yet one more way to level the playing field.

I don't buy the objections to the splits. They are a red herring.

Not quite - as the question arises "how do you power the mics"?

If you power the mics from one recorder and not the other you are skewing the results as one recorder does not have to supply the extra power.

Alternatively - if you use a 3-way split using the third way for power only and no machine supplying phantom power, then you are not testing to see if the extra current drain of providing phantom power affects the sound (although the two machines would be operating under identical conditions).

[bishopthomas]

Originally Posted by John Willett

Alternatively - if you use a 3-way split using the third way for power only and no machine supplying phantom power, then you are not testing to see if the extra current drain of providing phantom power affects the sound (although the two machines would be operating under identical conditions).

This is not what the test is about. Testing if a pre's phantom power affect the sound should be done with only that pre. External 48v supply vs internal. You don't need other preamps/recorders in the mix to test this.