I always enjoy hearing audio comparisons posted by others on this site, and I thought I would share a few interesting samples with you. I was recording trumpet today and doing a test of some different equipment and microphone positions.

The two clips provide an interesting comparison of the Forssell SMP-2 and the AEA TRP preamps. Both clips were recorded simultaneously.

The room is fairly ordinary. The two AEA R84s were arranged as close as possible next to each other (see picture), with the trumpet aiming between the two microohones. The ribbons were 9in from the bell edge, and directly in line with the bell. (Out of all my R84s, these two microphones are very closely matched, and are often used as a pair.) One microphone went to the SMP2 (using the Direct Coupled (DC) inputs) and the other to the TRP. Both preamps fed a Lavry Blue convertor, and were recorded at 24/96 using Sequoia. The levels were level matched as close as possible at the preamps, but were adjusted a few tenths of a db afterwards in Sequoia to get closer, and the files have been converted to 44.1/16 so that I could upload them here.

Enjoy!

Thanks for the files! The ribbon mics give a really nice sound on trumpet. I'm able to detect a very faint difference between the two WAV files. I couldn't really tell you what exactly it is, but there is something I'm picking up on that I don't think I'm imagining. Neither one is preferable to my ears though, which is especially interesting given the massive price difference between the two preamps.

Very interesting to listen to. I think the AEA definitely holds its own in this comparison.

Do you really think that two short mono (!) files would tell you something about the devices ? What kind of difference would you expect ? One thin, distorted with drops, the other full, opulent, clean ? heh There is a definite difference between these two preamps (I had both here), but you would have to work with them in real situations ... Then you would realise that the price difference is more than justified ...

Not surprising, since the TRP was designed by Fred Forssell!

smp-2 all the way!

I prefer the TRP.

hehheh

I didnt hear much of a difference at all.

IMO the SMP-2 hears more of the room and air around the trumpet, and many harmonics off that bell the TRP just doesn't get.

In a mix the TRP may put the trumpet more forward because so many nuances are pushed back or not present at all, yet it may also impoverish the mix if an acoustic sound is desired.

Mono is a very stable format for AB and ABX evaluations.

Without some serious controls, a stereo format cannot provide listeners with neutral information for objective analysis. Yet a worthy stereo test could be done with widely spaced microphones if frequencies above those affected by combing were isolated for comparison.

Acoustic engineers will tell you that, while stereo has more information, it is subject to all kinds of random factors in playback such as phase cancellation, comb filtering, and so on. These can also excite reactive differences in the playback chain, or frustrate truly objective comparison when the listener simply moves their head a few inches either way between speakers.

I would not want innocent random factors to skew anyone's objective evaluation. IMO, if we cannot hear a difference in mono we should give up doing audio professionally.

It's like the two views a man has of his bride on their wedding day. Stereo is how she looks at the altar in a magnificent dress with finery. What a sight! Mono is how she looks later the same day in their hotel room. I had to choose between the two, the bride in mono is more interesting, she reveals more details because there are fewer distractions, though she does deserve in that manner a very attentive, active listener.

My view is that mono as such is very unnatural and handicapped capturing and recording of the real sound source. We have two ears to perceive all the sounds of this world and two eyes to perceive the images. If we use only one ear (mono), the original sound is deformed and one dimensional, loses the depth and reality. If we use one eye, we lose the perspective, all the objects seem to be in the same distance ... Mono is just imperfect by its nature ... and not very nice sounding too ... But of course, this is a general thought (since you opened it), nothing about this comparison itself. If I want to see you, I would not close one eye, if I want to hear someone or nice music, I would not close one ear ...

With sufficient controls AB/ABX stereo tests can be as valid as a mono, but acoustics are what they are.

Yes, our ears and eyes are each two, but recording is not a perfect translation from a source to us so great care is needed in transmission to keep our eyes and ears from being affected by distracting and irrelevant artifacts. Remember, the goal is to understand how the gear performs, not how our eyes and ears perform when being entertained.

Since I'm in the mood for analogies: Stereo is like a 3D movie. To get the excitement of spacial depth the signal is distorted in nonlinear ways. While this has great entertainment value not all our perceptions are accurate, so we should not trust them enough to make claims about the quality of one stage or another of the transmission gear. AB should be a test of gear versus gear, not gear versus ear, or one person's ears versus another person's ears. Narrowing the subject of study by using a mono channel is a helpful because it focuses our study on the gear itself, minimizing the effect of acoustic energies that depend on uncontrollable variables in the playback system.

P.S. I think your approach to this is understandably informed and biased by the fact that you, like many long-time audiophiles, have a well-known chain of that has become your reference baseline. It takes time to get that kind of a system, and it is usually peculiar to a person. Pros often have a well known monitoring chains that functions this way. It is not a scientific approach because the "controls" don't work for others hearing the same clips. Mono signals focus more like a microscope on the factors under test, and because they are not subject to acoustic distortions resulting from stereo recording and playback, they are truer. You just have to be listen intent and focus.

thumbsup exactly what i heard! i was just to lazy to write, TRP sounds good but very dry and a little one-dimensional

Glad you have all enjoyed the samples!

To answer a question I was asked via PM: The right knob on the TRP (level potentiometer) was set to the upright detented position.

Also, I don't remember the exact number for each, but the gain on each preamp was set to a similar amount, in the 30-40db area.

Wow, did you do this sighted or blind? Can you really tell these two clips apart in an ABX?

Fran

i'm not michael and i did not do a blind test but i'm sure i can hear it and i think basically everyone could with proper monitoring and room treatment. i'm listening on focal twins in an ok treated room. how do you monitor?

I'm using a Hafler P3000 into a pair of Dynaudio BM6Ps. The room has some treatment installed, more on the way.

When I downloaded the clips I thought they were pretty hard to distinguish, so I dug up a digital audio player called "foobar2000" that includes an ABX tool. Loaded up both clips and started listening ... when it came time to decide call for X and choose it's identity, I had no clue whatsoever. I sure couldn't hear any difference in air, room, or harmonics off the bell.

What pointers could you offer, what detail should I focus on to discriminate between these?

Thanks,
Fran

Fran,

No, I don't have time or energy to do real ABX testing, I just listened to the clips back and forth several times, knowing which was which. I agree with futur2 that the difference isn't hard to hear with decent monitoring.

"ABX" came up in my ongoing discussion with Ivo of mono vs stereo sampling to evaluate gear. I appreciate his approach and we both manage to feed a friendly dispute over methods, at least enough to keep it alive from one thread to the next.

P.S. I visited your site today and spent some time enjoying a few clips of your guitar pickings. Very nice. Thanks!

Using these clips as an example, my comparative listening often goes like this: I ask what is there in the sound of the instrument (here it's a horn) and make a memory of it, playing both clips back and forth to really know it's own sound. Then I keep playing back and forth with the question in mind, what is physically behind that horn, what gives it a 3D-like relief in the sound stage? I try to see it physically in the space, yet with my ears.

In the TRP clip the horn is beautiful and very naked, the background around it is more in recess, I hear less of the room. But the horn is beautiful, metallic. The body is resonant and ready to reach out and be grabbed.

In the SMP-2 clip I hear more information coming from the horn but it's not first obvious what. It sounds like there's more room in the sound as well, but not sure what. Then I noticed more air immediately around the instrument vibrating like a soft sympathetic aura. Listening more closely it becomes quite clear that more harmonics are present in the SMP-2 clip that, by comparison, are a bit more muted in the TRP clip. The SMP-2 clip also caught more sound from the room.

I listen first to fundamental tones, but staying there I can't discern the subtler background, the nuanced secondary emanations. For me it always starts with the instrument, then I go back and forth between hearing it and what's in the background -- like grasping the instrument then reaching for the silence behind it.

This way I'm able to discern not only what else comes off the instrument besides fundamental tones, eventually even walls in the room may come into focus. Not knowing where walls are physically, there are often enough sonic clues to get a comfortable mental picture of the space, i.e. the sound stage, the instrument's place in it, and a feature or two of the larger room.

I had a simpler take on the comparison, but agreeing with most of the conclusions: Two outstanding preamps of similar sonic character, one slightly more nuanced than the other. Definitely familial.

Since acoustic-electric transducers are by their nature less precise than electronics, and since the two mics occupy different space and therefore pick up different signals, why does it make sense to ascribe the differences to the preamps rather than the mics and placement.

Fran

Valid points Fran!

And people, pliiiz do the ABX..


/Peter

I agree that Fran raises some interesting questions. There are severable variables at play here: different preamps, different mics, and different mic placement.

It's very hard in this case to say which are influencing the sound. I'm not one to talk too much because I can't even hear a difference between the files. Still, to those that do hear something: can you say for certain that it's the preamp that is making the difference?

I've been looking into this a lot recently and listening to tons of audio comparisons. From what I've observed so far the behavior of various preamps under close to ideal conditions is virtually identical. Electricity comes in one end and goes out the other in a seemingly predictable manner from brand to brand and model to model.

I believe others when they say they hear a difference. I understand that some preamps have extra features or behave differently under more complex circumstances, and that makes them more valuable. For example, the AEA TRP doesn't have phantom power, so that makes it useless for condenser mics.

Still, I'm a little perplexed at the myriad options out there for something as simple as amplification. I also wonder about all the strong opinions that people have about various preamps, especially since my experience (limited though it may be) tells me that the differences are miniscule.

As regards the factors in play, I think you raise excellent points of caution.

I'm trusting the OP's claim that the mics are closely matched and as I judge the session photo there should be little acoustic difference between them, as they are nearly coincident. I'm also assuming that the wall behind the mics is similar for both mics, and at 90 degrees they'll null out a lot of side wall. Reflections blocked by the player's body could be a significant factor in the room sound. As a ratio the bell is very close to both mics so ignoring the room sound entirely there remains a difference in harmonics emanating directly from the instrument.

Michael,

the question is how closely matched.. also I would not call the positioning concident. Even if you can "hear thru" the basic room character you can not hear thru discrete early reflections and those will likely differ between the mic's.


/Peter

My characterization of mic placement was "nearly coincident." The reflections from rear of the mics should be almost identical.

The important reflections, as I see it, would come from behind the trumpet player, blocked by his body. That factor could, I think, make a difference just as you say - especially if the room is small and the wall is reflective.

Listening via Mac audio out and a pair of AKG's, the SMP sounded better (and that's not exactly a resolving system, though the headphones are nice). However what I CAN tell you is, having spend some time with both preamps (and currently as an owner of 4 channels of SMP-2) is the TRP is incredible value for the money but can't touch the SMP-2 when it comes to how smooth the SMP-2 is. I found the TRP to be great but have a touch of grain. The SMP-2 was everything I liked about the TRP (tons of gain, works well with ribbons, not clinical) but eliminated that slight bit of grain I heard and that turned me off. For that matter, for what they deliver, BOTH units represent pretty amazing value from a cost-performance standpoint. My 2 cents.

I'm a simple amateur here, forgive my presumption. When I examined these files in Adobe Audition they displayed different volumes and different volume envelopes. The Forssell has lower peaks and higher RMS.

So either the mics and placement led to that effect, or the Forssell is functioning as a compressor. And compressor=THD. And the Forssell has vanishing THD, right?

So the difference is more likely due to the mics and positions than actual differences in the electronics, since transducers are orders of magnitude less accurate and less precise than electronics.

Fran

Fran, I agree that the transducer is typically much more variable from one to the next than solid state electronics.

You've taken some interesting notes on the PCM data. What differences (numbers) do you see in the peak and RMS amplitudes?

I'd be interested in hearing more details as well!