I just got an email from Apogee announcing their Duet2. In the highlights of the product description it states:
Better Sound Quality

On the specs on their website they state better sound quality as this

Sound Quality Duet = 1st Generation Duet 2 = 2nd Generation

I dont think I have come across the term 1st generation and 2nd generation quality sound. When they release V3 will it be 3rd generation sound quality> Will we eventually reach 100 generation sound quality in the year 2045. Man , I cant wait to hear what sound will sound like then.

Quite honestly I think this is all BS. Not just Apogee, but the lot of them whether it be software or hardware companies.

Im sure they can state a tiny margin of difference in the specs of the Duet 2's conversion or audio output or some esoteric thing which no one even knows exists and will say that means its better sound quality. But im pretty sure 99.999999999.9999% of ears out there will never hear any difference.

Seems that they are saying they've done quite a bit to improve the audio quality.


What's New?
- Completely redesigned mic preamps and converters

Better sound quality.
A difference you will hear.
Using the very latest technology and drawing upon the experience of developing Apogee’s new flagship audio interface, Symphony I/O, Apogee engineers rebuilt Duet to achieve a difference you can hear.

From the mic preamps to the AD/DA converters, Duet 2 offers the best of everything Apogee, allowing you to capture your audio with even more clarity and dimension than the original Duet. This is professional sound quality you can take anywhere.

Smooth, detailed world-class mic preamps
The Duet 2 mic preamps feature a new design, all new components and seamless click-free transitions as the gain increases and decreases throughout the incredible range of 0-75dB. This unprecedented feature allows you to dial in the perfect level while delivering ultra-low noise and smooth, crisp detail. Most importantly, the Duet 2 mic preamps are optimized for any sound source, so no matter what you are recording you’ll capture every detail.

Pristine, next generation AD/DA converters
Much like the mic preamps, the Duet 2 AD/DA converters are an all-new design and deliver the purest recordings and best listening experience possible. This totally new design takes the personal studio to the next level with state-of-the-art components and next-generation conversion.

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It seems fairly clear that they are saying the key audio electronics have been redesigned and improved. Of, we are mostly talking a few per cent improvement - you're unlikely to want to throw away your existing Duet and get a Duet2 and notice a world of difference. However, improvements are improvements, and presumably the original Duet will be discontinued.

Or are you saying that doing better, and improving your product is pointless in general? Or are you just calling them liars? :shrugs:

Im not saying improving a product is bad..of course not. neither am I calling them liars. But dont kid your self on Demsond. Marketing these days is everything. The smallest insignificant detail or so called improvement can be worded in any way they like to make the gullible masses believe anything they say.

What Im saying is I dont believe the improvements in
the convertor would be noticeable at all.
Perhaps someone with the most excellent acoustically treated room and most excellent speakers could tell a difference at a push.

I'm NOT talking about mic pre amps. Im taking about monitoring and recording line input sources.

Your taking Apogees word there's a noticeable difference and this of course is exactly what their banking on. But that difference could be an improvement way down in the noise floor (like -96db) which no one could possibly hear. Its like Dither. No one can actually hear it doing a damn thing yet some will say I prefer Dither mode fantasy 3 for its deep wide analog style sound. Do you hear Dither working when truncating a 24 bit file to 16 Desmond?

In a blind test nobody on this forum would hear the difference between the two Duets monitoring the exact same song. Yet , we will soon read reviews of a much more open , wide, deep sound etc blah blah. All of it will be Placebo effect.

Quote desmond:

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Seems that they are saying they've done quite a bit to improve the audio quality.

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i'm just waiting for them to make the same improvements to the Ensemble now!

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hourglass | random thoughts | doubledotdash!? collective

Quote Rob456:

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What Im saying is I dont believe the improvements in the convertor would be noticeable at all.
Perhaps someone with the most excellent acoustically treated room and most excellent speakers could tell a difference at a push.

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So you don't believe anyone will hear a difference... except those with good monitoring envirnoments who might!

However, I agree with you that modern converters and implementations are generally so good that incremental technical improvements are often extremely subtle, and superb monitoring environments are now required to really appreciate them.

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Your taking Apogees word there's a noticeable difference and this of course is exactly what their banking on.

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It would be a foolish company that made bald claims they couldn't back up, although I suspect the major audible improvements will be in the preamp performance, rather than the converter performance -- although having said that, clocking can have a radical affect on converters and small improvements there can be surprisingly audible.

I've not heard the Duet 2 yet, so this is only speculation on my part, of course.

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Its like Dither. No one can actually hear it doing a damn thing yet some will say I prefer Dither mode fantasy 3 for its deep wide analog style sound. Do you hear Dither working when truncating a 24 bit file to 16 Desmond?

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I don't know about Desmond, but I have certainly heard differences when switching between different dither algorithms -- the results are very dependent on the material being processed: some makes the differences far more audible than others.

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In a blind test nobody on this forum would hear the difference between the two Duets monitoring the exact same song.

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You might well be right...

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Yet , we will soon read reviews of a much more open , wide, deep sound etc blah blah. All of it will be Placebo effect.

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Let's wait and see, shall we....

hugh

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Technical Editor, Sound On Sound

No argument on the marketing side. But there's a number of real functional differences between the units.

http://www.apogeedigital.com/products/duet2.php#chart

According to MusicRadar, list price on the Duet2 is $595, and you could reasonably expect street price to be $50 less than that. Amazon.com has the Duet1 at $495. Given that there's a bunch of new features even before you consider the audio path, is this such a big deal?

The first thing I noticed in the specs is lower latency, which is always welcome!
Other than that, there's little to make me upgrade from my 1st gen Duet. I really need more IO now anyway, so i'll need to look at something else altogether..

Paul

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Paul

Quote Hugh Robjohns:

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Quote Rob456:

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Its like Dither. No one can actually hear it doing a damn thing yet some will say I prefer Dither mode fantasy 3 for its deep wide analog style sound. Do you hear Dither working when truncating a 24 bit file to 16 Desmond?

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I don't know about Desmond, but I have certainly heard differences when switching between different dither algorithms -- the results are very dependent on the material being processed: some makes the differences far more audible than others.

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'Hoping that this is not a complete hijack, but since the subject is already under discussion:

My impression is that dither is supposed to be sufficiently randomized that it has no effect on program material. Is that correct, or "not really"? If dither algorithms can so change a sound, it's hard to believe that dither does not distort the program material, and is this always better than "self dither" + truncation?

I, too, hear the difference that different dither types produce, and it bothers me that dither often seems more like a wild card than a transparent necessity.


EDIT: Sorry if the quote level is off-I worked on it but .......

"....even more clarity and dimension..." says it all really!

Sigh, 4 colour glossies in the prosumer game always make me wince, that sort of empty statement blongs on mr Andrew's site not in the sales material for a allegedly professional product.

Seriously, when did pro audio companies start emulating bloody audiophool targeted marketing.

To add insult there do not actually appear to be any real specifications available...

24 bit, but where is the noise floor, what is the full power bandwidth, large and small signal frequency response? At various gains? Mic preamp noise figure?, a 2 tone IMD plot would be nice....

All this stuff is missing, instead we are told it has "even more woo" then the last one that also lacked all the above...

It looks to me to be almost targeting the "Lifestyle" market rather then the "audio Engineering" one.

Nope, not convinced to buy one.

TBH, converters are a mostly solved problem (or at least, essentially everyone has the same unsolved problems, and nobody talks about them), so commercial state of the art now holds very little interest.

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Rob, I am a little more skeptical than others, especially when these sorts of things are said:

"Most importantly, the Duet 2 mic preamps are optimized for any sound source, so no matter what you are recording you’ll capture every detail."

Wow, optimized for any source! What the heck does that mean? Flat, colored, nicely colored, flat with spice, or how about "completely neutral and warm with soul?" Don't laugh, the last one comes from a major manufacturer.

What is optimization anyway, and does this mean that the last Duet had preamps that were optimized for something other than anything? What were the preamps in the last version of Duet optimized for?

A for "a difference you can hear," that tells me that the product will be different, but not necessarily better.

(It's very hard to avoid mentioning the marketing spiel of a beloved microphone manufacturer, here; because the market speak is so similar and ridiculous-though what Apogee is saying is a little less oxymoronic than that from the mic manufacturer.)

I would bet there are changes mostly for the good in the new product, and most people will prefer the new sound. But that doesn't mean that you will. We'll all have to wait for the product.

Personally, I'd like to see them bring back products like the "Mini-Me", which offered more independent operation and much more flexible mating with a wide variety of devices.

Well, sound quality is very good and good enough on my Duet. I think that the big improvements are
1: the oled screen, and that
2: it is a USB thing.

Negative is that
1: it doesn't have separate mic and instrument inputs..!
2: It still doesn't work on more platforms.

The RME babyface is, I guess, by far a better option than those two, but it's also more costly.

Still, I'll stick with my Duet.

Quote Jeraldo:

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My impression is that dither is supposed to be sufficiently randomized that it has no effect on program material.

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Simple TPDF dither has a flat frequency response and so has a negligible affect on the character of the audio, other than in preventing truncation distortion.

However, noise shaped dither algorithms, like POW-r, UV22, SNS3 and others are exactly that: noise shaped. Most dump a substantial amount of noise in the HF spectrum, and that can most definitely interact with the source material in some cases to change the perceived character of it.

Since different noise-shaped algorithms dump the energy in different parts of the spectrum, different algorithms will produce different results with different styles of music.

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If dither algorithms can so change a sound, it's hard to believe that dither does not distort the program material, and is this always better than "self dither" + truncation?

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'Distort' isn't really the right word to use given that dither is specifically added to prevent quantisation distortion. But I think it fair to say that different dither algorithms can affect the perceived tonality of a track. It's not always audible, but it can be...

You can sometimes get away with simple crude truncation and 'self dither' if the recorded material has a significant and consistent noise floor, but not if you want to include fade outs!

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I, too, hear the difference that different dither types produce, and it bothers me that dither often seems more like a wild card than a transparent necessity.

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Then stick with TPDF dither which is totally benign. The only advantage of noise-shaped dither is a quieter perceived noise floor... but that's utterly irrelevant if the source recording has a high ambient noise floor anyway!

hugh

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Technical Editor, Sound On Sound

Quote dmills:

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It looks to me to be almost targeting the "Lifestyle" market rather then the "audio Engineering" one.

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That'll be because they are aiming it exclusively at MAC users to whom 'lifestyle' is the only style, and most home recording musicians do it as a lifestyle choice.

Audio engineers in the sense you mean are very thin on the ground these days... Few Apogee users would know what to do with an IMD plot unless you folded it into a interesting hat first!

hugh


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Technical Editor, Sound On Sound

Quote Kaw-Liga:

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Well, sound quality is very good and good enough on my Duet. I think that the big improvements are
1: the oled screen, and that
2: it is a USB thing.

Negative is that
1: it doesn't have separate mic and instrument inputs..!
2: It still doesn't work on more platforms.

The RME babyface is, I guess, by far a better option than those two, but it's also more costly.

Still, I'll stick with my Duet.

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Check out the feature set for Sound Devices USBPRE 2. It is unlike either the Duet or babyface, and it either "hits" you needs or not. Here, more expensive than the Duet, significantly less expensive than the babyface.

Let's see-Sound Devices and lifestyle vis-à-vis Duet and babyface: I guess that would be "retro geek". Seriously, it's a real piece of hardware.

Surely anyone wise enough to know better can see through the marketing speak. There's a different to genuine listed improvements and the "generation 2 audio" thing which is really just a non-technical way of saying the new product is better - as most proespective users at this level probably wouldn't want to read frequency response charts and distortion figures.

Anyone who doesn't know better has a learning curve to go through...

"Please buy our new product! It's exactly the same as the old, it just looks newer!".

Dilbert comes to mind, here...

Thank you, Hugh, for your comments about dither, presented in understandable and succinct form as usual!

The thing about dither is that some of it is expressly designed to have an audible effect!

Straight TPD just raises the noise floor but once you start looking at the more extreme noise shaped efforts, let alone at "dithers" which are expressly intended to have a sonic signature then all bets are off really.

I am not at all surprised that something which packs significant energy into the (just) ultrasonic region might cause some downstream get to exhibit audible non linearity for example. It shouldn't, but somehow you never see high frequency two tone IMD measurements for run of the mill audio amplifiers, let alone something like a class D amp in a set of monitors....

Regards, Dan.

Whoops, Hugh got there first.

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Audiophiles use phono leads because they are unbalanced people!

Edited by dmills (31/03/11 04:04 PM)

Quote Hugh Robjohns:

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Quote dmills:

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It looks to me to be almost targeting the "Lifestyle" market rather then the "audio Engineering" one.

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That'll be because they are aiming it exclusively at MAC users to whom 'lifestyle' is the only style, and most home recording musicians do it as a lifestyle choice.

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Have a look at the box for the RME babyface-and the product itself- and try to figure out who that's being marketed toward!

Sorry for grammar..

Quote dmills:

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Whoops, Hugh got there first.

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Appreciated, nonetheless....

Quote Hugh Robjohns:

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... Few Apogee users would know what to do with an IMD plot unless you folded it into a interesting hat first!

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Thanks Hugh, a candidate for the quote of the year

Andy

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When the going gets weird, the Weird turn Pro.

I've been web searching, trying to get a grip with 'Intermodulation Distortion' and IMD measurement A4 paper hats.
Pretty serious stuff - way beyond my origami skills - i grabbed this quote from a pdf (IMDanREVc.pdf) on the issue of IMD.

''This is a very real and legal issue for equipment makers and renders this measurement of significant importance.''

Intriguing!!

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.. is this thing on?

Edited by Stan (01/04/11 02:01 AM)

Doh,,,I knew I shouldn't have mentioned dither
I suggest that what your hearing is placebo.
If you really are hearing a difference turning your dither plugin
on and off then don't use it. Of course that completely goes against what all the specialists say...
Try a simple test. Render a song without dither and one with and try and set up a blind test system. See if you can tell which is which.
..............................................

The new and improved Duet will not sound any better than the original(not talking about mic pres btw). Im not attacking Apogee or suggesting they are liars. All companies do this to sell their repackaged products.

Ive got a number of converters here ranging in price from cheap to a lot less cheap and straight up no BS I cannot hear any difference between them. Sure there will be a difference but its so minuscule it doesn't even register. The same will apply to the Duet2

Lets not forget that many "upgrades" are in fact cost cutting measures by the manufacturer.

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My head hurts!

Quote Rob456:

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Try a simple test. Render a song without dither and one with and try and set up a blind test system. See if you can tell which is which.

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If the ambient noise floor of your recording is substantially above the 16 bit system noise floor of -93dBFS (and almost all will be) then that noise floor will swamp the dither entirely and you are unlikely to notice any difference between straight truncation and a properly dithered truncation (although some heavily noise shaped dithers may have an audible affect because of the additional HF spectral noise content).

However, if you include a slow fade in and fade out in your test, you will most definitely notice the absence of dither, and the inevitable truncation distortion in the undithered version will become readily apparent at the quieter ends of the fades.

Quote:

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All companies do this to sell their repackaged products.

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To be fair, the Duet 2 is rather more than simple repackaging. The fact that it now has balanced outputs implies a complete redesign of the analogue output stages, and we know the mic preamp (and probably the line input stages) have been totally redesigned too... so it doesn't seem entirely unreasonable to me to think that there may well be an audible difference between the two units -- albeit a pretty subtle one.

But without actually listening and comparing the two units in a critical monitoring situation this is all pure speculation and an utterly pointless discussion.

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Ive got a number of converters here ranging in price from cheap to a lot less cheap and straight up no BS I cannot hear any difference between them.

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I've no idea what you consider to be cheap and a lot less cheap. All I can say is that there certainly are very audible differences between budget and high end converters. Differences are far smaller at the lower end of the budgetry scale, generally because the limited performance of the analogue stages swamps the potential capabilities of the converters. Added to which the inherent limitations of budget monitoring and poor listening environments will make it impossible to hear subtle differences between designs.

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Sure there will be a difference but its so minuscule it doesn't even register. The same will apply to the Duet2

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I agree... I suspect the audible differences between the old and new duets will be very small, and probably irrelevant to the potential purchasers... but that's not to say there won't be audible differences.

As I said earlier, this is a pointless discussion since none of us has been able to compare the devices being discussed. Moreover, the improved feature set of the new model and the withdrawl of the old model means that potential purchasers will only be able to, and want to, buy the new model anyway.

Hugh

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Technical Editor, Sound On Sound

OK so I have a question relevant to this whole discussion. I have been mixing using Samson Rubicon 5a's and a Presonus Firebox. Recently we upgraded the interface we use for recording in the home studio (a different location to where I mix) from a Presonus Audiobox ( we were using a Korg 8 track to record drums) to a Presonus FP10 (previously called a Firepod I think). Anyhoo, after it was all set up and we were listening back to some mixes I couldn't help but think that everything sounded a lot better, which is interesting because I wasn't expecting it to happen and I hadn't paid any money for the interface so didn't have a wishful thinking bias. The only reason we got it was because transferring files from the Korg to the Mac was a pain and the FP10 has 8 xlr inputs. So you see I was psychologically primed to hear a difference, I was genuinely surprised.

Anyway, the point is after this I was thinking I should upgrade to a better interface in my setup (where I'm only really mixing now) to get this improved D/A conversion. I was thinking about getting the Apogee Duet (I'm not rich) but was reading about some issues. Anyway, after reading this whole thread I'm really confused as to whether I just imagined this improvement that I heard, and whether moving to the Duet is worth it at all?!?! I would really appreciate some input on this, thanks!

Quote onesecondglance:

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Quote desmond:

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Seems that they are saying they've done quite a bit to improve the audio quality.

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i'm just waiting for them to make the same improvements to the Ensemble now!

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Ensemble soounds great. Its bloody Maestro that needs a whole re-write. Most irritating software.

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I'm All Ears.

Quote zenguitar:

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Quote Hugh Robjohns:

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... Few Apogee users would know what to do with an IMD plot unless you folded it into a interesting hat first!

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Thanks Hugh, a candidate for the quote of the year

Andy

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quite, i'd frankly add that few of said users would know what IMD stood for....


but leave of the Mac user bashing Hugh..... some of us couldn't give flying F**K about "lifestyle" but choose to use tools that work more often than not, and more relevantly, are the only tools available for some situations.... like running DP or Logic.... a necessity , not a choice, if you happen to be working with a client that chooses to use those DAW apps

as to when Pro audio companys started marketing like this..... waaayyyy back, when they realised that they could only bring products to market if they sold enough of them to sensibly recoup development costs.... or else they'd always be on the brink of financial ruin....

I quite enjoyed the Mac bashing actually (Mac user myself) although take your point that it is an essential for logic based folks and improved general workflow - and so much cooler!

Quote buggymusic:

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I quite enjoyed the Mac bashing actually (Mac user myself)

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Agreed, from another Mac user and Duet user (only version 1 though...)
Wee bit of humour is always welcome.

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Cubase, guitars.

Quote buggymusic:

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and so much cooler!

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see you were doing fine right up to THAT moment......



they're not cooler, they're tools.....

( must...... fight....... the..... urge...... to say "cool tools" ARGHHHHHHHHH )

Nice Mac. Nice DAC. Nice Food. Nice Drink. Nice Van. Nice Mics. Nice Headphones ... Yup, I like stuff that works well and is nice to Be With. Oh, and Nice Teasing, too!

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PA stuff on FB

Quote desmond:

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Surely anyone wise enough to know better can see through the marketing speak. There's a different to genuine listed improvements and the "generation 2 audio" thing which is really just a non-technical way of saying the new product is better - as most proespective users at this level probably wouldn't want to read frequency response charts and distortion figures.

Anyone who doesn't know better has a learning curve to go through...

"Please buy our new product! It's exactly the same as the old, it just looks newer!".

Dilbert comes to mind, here...

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The marketing material is based on the fact they're using newer converters and pre amps. And also running off USB instead of Firewire which means it's a new design. Subjective impressions on other forums say the AD/DA is alot less 'coloured' than the original Duet.

Edited by Nites (16/11/11 10:48 PM)

Quote Hugh Robjohns:

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Quote dmills:

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It looks to me to be almost targeting the "Lifestyle" market rather then the "audio Engineering" one.

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That'll be because they are aiming it exclusively at MAC users to whom 'lifestyle' is the only style, and most home recording musicians do it as a lifestyle choice.

Audio engineers in the sense you mean are very thin on the ground these days... Few Apogee users would know what to do with an IMD plot unless you folded it into a interesting hat first!

hugh

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Yes. And refrigerators are fascinating in their design also.

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I'm All Ears.

Some interesting engineering tradeoffs in designing those things to be sure .

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!

Well, refrigerators must be cool ...

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PA stuff on FB

There's a clear improvement in the micro-proprieties of the coating...

Quote Hugh Robjohns:

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Few Apogee users would know what to do with an IMD plot unless you folded it into a interesting hat first!

hugh

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I prefer to make a snood out of mine!

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Google less; read more!

First Post here!

To much talk - let us listen to these very impressive tests on you tube -

Apogee DUET 2 Vs Apogee Rosetta 800 + API 3124 with Beyer M160 Ribbon Mic - (A B between them) WOW!

http://www.youtube.com/watch?v=c1gYvvAI_NA&feature=mfu_in_order&li st=UL

Duet 1 vs 2 -
http://www.youtube.com/watch?v=3gyqiwxJY4w

Remember to listen in HD!

I think im sold for a portable..

Well, the second track in the second vid is louder ...

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PA stuff on FB

Quote Baboo808:

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First Post here!

To much talk - let us listen to these very impressive tests on you tube -

Apogee DUET 2 Vs Apogee Rosetta 800 + API 3124 with Beyer M160 Ribbon Mic - (A B between them) WOW!

http://www.youtube.com/watch?v=c1gYvvAI_NA&feature=mfu_in_order&li st=UL

Duet 1 vs 2 -
http://www.youtube.com/watch?v=3gyqiwxJY4w

Remember to listen in HD!

I think im sold for a portable..

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There is one more A/B test here, between the Duet II and the RME Babyface: http://www.youtube.com/watch?v=-ur6UmY0M60&feature=results_video&p laynext=1&list=PLA164785AAB4B4CFB

Much as I would love to get the Duet II (being a MacBook Pro user), the concern I have with ALL of the videos above is that the Duet II sounds "scooped" compared with the Rosetta, the Duet 1 and the Babyface. It's as though there is a smile curve applied, and it is the highs in particular that seem to stick out compared to the others. In the Duet I vs Duet II video I much preferred the Duet I as being less hyped (although of course I was not in the room to hear the actual instrument!).

What I cannot figure out is why Apogee would release a product as an improvement, yet the sound samples I have heard seem to indicate that this may not be an improvement in so far as it sounds scooped.

Any thoughts? I a struggling between the Babyface and the Duet II...

Len

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www.youtube.com/leonardngmusic

I am too scared to ask what an IMD plot is, so I am just going to google it.

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Instant gratification is actually pretty good. It's fast as well.

I just googled IMD plot, and got:

"... hence, if one plots P out (fundamental) and P out (third order product) as a function of P in, the slopes of the curves will be approximately 1:1 and 3:1, respectively, at sufficiently low power where the system is linear. With these disparate slopes, the lines will eventually intersect and the point of intersection is termed the third order intercept point (TOI). The amplitude of Pout (third order) relative to P out (fundamental) at a given input power level is termed the IMD level. These concepts are illustrated in Figure 2."

I wonder if the bloke who wrote that has a T-shirt saying "It's only rock'n'roll but I like it ?"

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Instant gratification is actually pretty good. It's fast as well.

There's a series of Babyface vs Apogee Duet 2 comparison videos on Youtube. At the end the guy says he believes the Babyface is better value, because it has more features overall and is expandable if you need more input channels in future. Also alot of people seem to agree that the Duet 2 conversion sounds more 'colored' or 'flattering' with that Apogee sound, whilst the Babyface is much more flat and true to source.

I can vouch for the RME drivers they are rock solid, have excellent low latency performance and are feature rich.

Sam,
I don't see anything particularly unclear about that statement (And rock is just blues with attitude, but I like it!).

Getting WAAAY off topic.

What that guy did not say is that third order law (That 3:1 relationship) breaks down at high level, which is interesting information in itself as it tells you not only how linear the system is at low level, but where it starts to distort further.

Further the 3:1 relationship is interesting in that it means that the level of the third order products is 3 times the difference between your working level and the third order intercept down.

So if for example I have some bit of kit with a third order intercept at say +40dBv (Third order intercept numbers are ALWAYS theoretical, you generally cannot get near them without letting the smoke out), and I am feeding it with say +10dBv peak then the distortion products will be at -90dBv, raise that to +20dBv drive and the distortion rises to -60dBv, +30dBv and we now have the distortion at -30dBv, a mere 40dB below the wanted signal.

The third order intercept is the point at which the third order product would theoretically be equal in power to one of the tones generating it (Third order law breaks down well before this point, but the number is useful none the less).

A fascinating thing to do is to take two speakers and amps and two sine generators (Or a good PC sound card) and set one to say 300Hz and the other to 700Hz, now take a condenser microphone and record some of the result, tweaking the amps to get equal recorded levels for both tones, plot the spectrum.

Do this at a few different levels, and watch as the third order distortion products(100Hz, 1100Hz, 1300Hz,1700Hz) come up scary fast with increasing level.
Even very good condenser mics are not particularly linear, which probably explains some of the added 'sizzle' that does not appear in a single tone frequency response plot.

Note the insidious bit, these distortion products are NOT harmonic distortion, they bear no harmonic relationship with either tone, also as you add more tones there is a combinatorial explosion and the number of products rises very, very quickly.....

Regards, Dan.

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Audiophiles use phono leads because they are unbalanced people!