600 vs 700 series stereo imaging test...

[Schuyler Monroe Hupp]

I just did some testing to compare 600 and 700 series recorders ability to render realistic, transparent stereo imaging.... I don't have a 744, but used a 702, and compared it to a 633. The mics consisted of two AT4047's in XY config, and also a MK41 & MK8 MS setup. Sources were voice & hand claps. Room was typical interior, with sheet rock walls, textured ceiling, carpet, about 300 sq ft.  RT60 about 500ms, mics set up where both early and late reflections were picked up... Monitoring was via both headphone jack and XLR outputs (ABing between the two) Heaphones were 7509's and Beyer 770's. An external headphone driver with Burr Brown IC's was used achieve much lower distortions than what are normally associated with headphone drivers.

Subjective results, at least to my ears and with this particular set up was that the702 has superb imaging:  Open, and natural sounding, with a clearly translated stereo field that gives one the sense of a real, three dimensional acoustic space, e.g. complex ambient reflections...   633 exhibited, at least in this experiment, wonderful response and clarity, but a not so well defined stereo field, not quite the sense of a real, three dimensional acoustic space as with the 702. Interestingly, the difference in stereo imaging capability was apparent in the input monitoring mode, as well as during playback, which indicates that some of the differences are in the audio chain, before recording has even occurred. My take on this is that the performance of the 702 with regard to rendering stereo imaging, is reflected in the distortion figures. In older gear I've tested, jitter was sometimes involved, but in this case, there is significant difference in THD figures that could account for the results.

 

Conclusion?    I would say that, contrary to what I've read in some forums, the 700 series is far from obsolete. They sound amazing! 

 

Next week I'm going to compare the 702, the 633 & the Zaxcom Maxx. 

[foss]

terrific. Thanks for posting this. Any chance of linking the files?

 

Cheers!

[John Blankenship]

Thanks for the tests. Looking forward to next week's results. Add a Nomad to the group if you can.

[VASI]

I did a project last Sunday with Sound Devices 702.

One take (steadicam), she signing A capella style (rebetiko).

 

Clean and natural sound.

 

[Constantin]

And you listened to the recording (playback) or the live input during a recording?

I'm ready to believe your results (purely because they confirm what I have thought all along), but perhaps you could compare the recordings on a computer. Unless you are really interested in the playback/output performance of these recorders. But I think listening on a different device (but same for both recorders) is more relevant to their intended use. It'll also eliminate more variables

[Tuhiva]

It seems more accurate to listen to the two files being played in an audio editing software (through same pair of speakers).

 

Also were the two recorders recording at the same time or it was two different performances?

[Schuyler Monroe Hupp]

Posting files of the test.... Yeah, that's a good idea.   Whether the test results can be heard would depend on the quality of your downstream chain though, but yeah, that would be interesting. 

 

I didn't hear any difference between the recorder line outputs and the headphone outputs. My ears are not that good.  However, I was using my own headphone driver at the end of the chain, to minimize distortion in that regard.

 

IMHO, the 700 series is far better in terms of fidelity, which I think is reflected in the distorion figures they publish, though of course the features and applications for the respective machines are different. 

 

...

[Schuyler Monroe Hupp]

 I don't have access to a Nomad, but will be receiving a Maxx in a week or so...   Do you reckon the analog chain and converters are the same in those two machines or not?  I'd love to see a schematic!   In fact, I'd love to see a schematic for any of this stuff.  I haven't asked, but my guess is that the manufacturer's would rather not hand out drawings for these things. I've done a few minor repairs on 702's and was really scratching my head trying to figure out where the front end preamp IC's were.  Those things are very tightly packed. Extremely well made.

[Glen Trew]

Was the comparison done with both the XY and MS on both recorders? How were the Mid and Side elements tracked? How was the MS recording decoded? Did the XLR outputs vary from the headphone outputs?

 

GT

[Schuyler Monroe Hupp]

The idea of comparing the two resulting test files on a computer is a good one, but so far as I know, the subtle nuances of timing that are involved in stereo imaging, beyond the slower amplitude differences, are not visible in the envelope, or even discernable to the human eye at the waveform scale, i.e. oscillosope.  At least for me, I have to either listen to it, or measure the distortion, and the set up for measuring distoriton at those low levels is very tricky, something that I don't have the gear for, so I rely on the manufacturer's claimed figures.  So far, the timing related stereo imaging capabilities of most of the gear I've used has a very tight correlation with distortion figures.   e.g. 663 says 0.09%THD  and the 702 says  0.004% THD and the 702 has much better stereo imaging.  Or, say for example, the ideal theoretical distortion of a 5532 op amp has distortion figures that are a couple of orders of magnitude higher than say, a TI/BurrBrown OPA2132 or an OPA227, and at least with my ears and my setup, the stereo image always sounds better with the lower distortion IC.   In a typical chain, where the op amp is not working hard to drive a load, this is not as big of a problem, but when driving say, a pair of headphones or a speaker, it can make a huge difference, at least from my experience. 

[Schuyler Monroe Hupp]

The idea of playing them back on monitor speakers is a good one; however, I don't have any audiophile monitors that are really capable of reproducing the timing dependent dimension of a great stereo image. I have JBL LSR4328P's and though they are an excellent reference monitor, they don't have much in the way of timing dependent imaging...  That being said,  loudspeakers never have as good a stereo image as headphones due to acoustical crossfeed, which tends to mask the image, though with a good near field monitor set up, with an early reflection free zone (at least with speakers better than mine)  you should be able to hear it~!

[Schuyler Monroe Hupp]

Having the two recorders going at the same time is cool, I like that!    When I get the Maxx, I'll see if I can set it up that way and then post the wav files.           I am really tempted to pop the cover on the 633 to see if it would be possible to improve performance by way of simple re-chipping, but I don't want to kill the warranty.  Maybe in a year or two I will disect one of those things...  :-)

[Schuyler Monroe Hupp]

This is pretty much a seat-of-the pants, practical test. Highly subjective, right? But I like the idea of splitting the mics to the recorders under test and keeping everything else the same.   So far, I am loving the sound of the 702 and the features of the 633.  Wish I could have both in one machine!

[Constantin]

The point of listening to both recording on a computer (ir at least the same pkayback device) is not so much to apply measuring equipment, but to have exactly the same playback specs. As I said earlier, these recorders were built to record and not so much to play back.

All the distortion figures you are quoting are for the inputs of the machines, the outputs are a different story. For an honest and meaningful comparison you have to playback in the same machine

[Jeff Wexler]

As Constantin points out, the playback setup is crucial. Since you are trying to determine things like "sound stage" and "stereo image", "space" and other nuances, the fact that many headphone amps in portable recorders have a miserable cross-talk spec, this throws all evaluations between recorders out the window.

[Schuyler Monroe Hupp]

The playback issue is an obvious and crucial one. So I'll see if I can get some good wav files and then compare them with the best playback audio chain I can put together, at very least, the -same- playback chain for both files.  What I do know is that just monitoring the inputs, I can hear a subtle difference, that the 702 seems better than the 633 in terms of stereo imaging.  BTW, I used the line outputs on both machines with my own headphone driver and the results of the tests were the same, with a stereo image from the 702 that just leaps out from the earphones...  :-P

[Jeff Wexler]

"At this point, I don't know. What I do know is that just monitoring the inputs, I can hear a clear difference, that playback reflects that difference, and that the 702 is in a different class, way better than the 633 in terms of stereo imaging."

 

I'm not trying to take the wind out of your sails and it is commendable and valuable the tests that you are conducting, but I do have one question: how important is "stereo imaging" for the work that the majority of us do in production? Considering the effort you have been going through to test the SD 633 up against the SD 702, what sort of recordings are you having to do, with either machine (other than the testing) where the stereo image is important?

[Philip Perkins]

I commend you on testing your gear and deciding what you like, but caution you about making statements like "X has much better imaging" without going the distance to make your testing more rational and repeatable.  Besides the effects of monitoring esp re head position, playback system, relative volume levels and the like there is the matter of observer bias.  The only way to really know the answers about things as subtle as what you are testing for is blind testing, properly done.  Richard Feynman said: "the easiest person to fool is yourself".

 

phil p

[Jeff Wexler]

+1 to Philip! Blind testing, particularly when trying to analyze the subtle nuances you are talking about.

[Matt Radlauer]

When the 6 series mixers came out it was very clear that the pre-amps were different from that of the 7 series, more like the 552. I'm not trying to debunk what your doing but because of the known differences the quality of the tracks are bound to be a little different. While the 6 series amps sound nice, the 7 series sound that much nicer...right?

 

I will agree with the rest when comparing two stereo images...blind testing of the tracks is the way to go, but also a recording of exactly the same source using exactly the same mics.

 

Mic placement and the source for your stereo image are going to determine how well the track images. Relying on the HP output of a field mixer is probably not the best way of judging the actual image..

 

When I did music I always loved soloing a set of drum overheads (spaced pair). Especially with a choppy drummer who moves around the kit. You could feel the movement.. Hearing the tonal quality of the cymbals or ride on one side of the kit (drummers perspective of course) compared to the tonal quality of the cymbals on the other side of the kit.

[Jon Gilbert]

What headphone amp did you use? I've been wondering about using one to improve my 664's headphone out.

[IBH]

From what I've read on THD, it is very difficult to hear a difference in anything below %1 THD (*except for when using pure sine tones). The 702 is rated at .004 max, and SD633 at 0.09% max, or converted to a dB rating,  -87dB and -61dB, respectively. 

 

Go into your DAW, load a file, listen to it, and then reduce its amplitude by 61dB, and tell me if you can hear it...you probably can not.

 

I'm not saying that THD isn't influencing some factors of the recording, but for stereo imagining I believe others factors would very quickly override the minute effects of THD, such as phase and timing differences between microphones, placement and even sampling rate. 

What I suspect is going on here is, as others have suggested, differences in the quality of the monitoring outputs of the two units. I'd be very interested in a AB double blind test.  

[Schuyler Monroe Hupp]

So I just finished a long test listen of the three machines and I just gotta say, they are all wonderfully engineered, just amazing how good they sound. Yeah, I recorded on to all three machines simultaneously with the same mics and then loaded all of the wave files on to each of three machines and listened to them closely. Still a totally subjective test.  Anyway, each appears to have its own character, varying degrees of subjective transparency, with some of those differences manifesting as ever so subtle variations in stereo imaging, and at least to my ears, in relation to time domain performance and the way that can affect the reproduction of complex reflected sounds in the stereo field.  If you can afford it, at least to my thinking, it would be nice to have couple of different machines to choose from.  Say, one for dialog and another for stereo field recordings?  The main thing I've learned is that the machines are all amazing and that the sonic differences are very small, so I would be happy to use any of them.

 

I will mention briefly that the subjective AB double blind tests that would indicate that people can't hear differences in distortion below a certain threshold, e.g. the popular 1% THD figure, is not valid, I think, in relation to stereo program material. When distortion manifests in the time domain, as differences phase in a stereo field, the human ear - brain combination, is capable of hearing very subtle differences, perhaps an order of magnitude lower than that, if not greater.  Monophonic, yes, the 1% figure is about right, but with regard to phase distortion in the context of stereo, it's considerably lower than that. 

[Schuyler Monroe Hupp]

I really like the headphone amps in all of the recorders, though my ears seem to prefer the one in the 702.  I also have outboard headphone amps that uses high performance op amps (OPA227 or 2132 for example). From my experience, driving the load is when a lot of distortion can be introduced, and that's where I've been able to improve my listening experience.  It is splitting hairs, I have to admit, but it can be fun to listen to!  There are entire web sites dedicated to building headphone amps. There's an ongoing debate regarding the subjective benefits of high performance headphone drivers too, as not everyone can hear the difference. I would say that if you can't hear the difference, or don't care, then don't bother, but if you can, then by all means!  At least for me, I enjoy having that little extra clarity, even if it is subtle (e.g. improvements in stereo image).

[Schuyler Monroe Hupp]

I love that Richard Feynman quote!  He was an exceptionally wise and rational man....   Yes, it's easy to fool ourselves!  It is also very difficult, if not impossible to describe subjective experiences to others who have not shared the same experience.  You can quantify things in many different ways, but they are all just dancing around the thing you're trying to share, if it happens to be a subjective experience.   Words are not the same as the things, but sometimes it's all we have.  :-)