Doing a lot in acoustical engineering the first thing I would do is plot the frequency response in the room. You could do a simple 1/3 octave plot, but this is probably a little crude for what you are looking for--still it would be a start. I would actually use an MLS method, which is a noise burst and the an FFT transform that would give me the plot. The other thing it would do is give me reflections in the room and timing of those as well as the frequency range that they comprised. Then I would look at the waterfall plot and see what the energy time curves were like in this frequency range as opposed to areas outside this range. This would tell me if the problem was room interaction or not. Cases like this I usually expect it to be room interactions--but not knowing the room or equipment it's impossible to say. Even if I did know the room and equipment I would probably first do some theoretical calculations and then proceed with actual measurements. |
Rives: What your are describing sounds like trying to measure the impulse response of the room.
1. What would you use as a noise burst source?
2. What would be your detector? I assume you would locate the detector at the listening position. [I can do an FFT in MATLAB, but need to get the time series data input to my computer to do the plots you describe]
3. What characteristic behavior would you be looking for in the waterfall plot? A more rapid decay of energy in this band?
4. What calculations would you make? Anything besides the peaks and nulls of standing waves? I have an irregular shaped room , but do have a program I use for SONAR development that would give me the normal mode structure for a room like this.
Thanks for the input. I would like to give this a go, as long as I have access to the tools I need to make the measurements.
Judith |
Elementary, my dear:
It could be your CD player -- piano is an instrument with many complex overtones. Many CD players (even expensive ones with favorable reviews) fail at trying to reproduce natural sounding piano music. violins, cellos, and even brass instruments are difficult for CD to get right. That's why many folks like analogue! |
Plato, Hate the thought, but hear the message loud and clear. As it happens, my CDP is an "even expensive ones with favorable review" player. Thanks. |
Judth: We use the ETF software a calibrated microphone and pre-amp from Germany, and couple all of it through a PC computer. This provides the noise burst. The detector is at the listening position, but we generally vary it with about 6 sequential measurements to get some averaging (but do not actually use an averagin function as it can be misleading) It's pretty amazing the measurements we can achieve today with about 1/10 the cost of hardware required only 5 years ago. You can go to our website at see the software and measurement tools we use:
http://www.rivesaudio.com/software.html
The kits we sell here are primarily for our dealers that take measurements for us, but do still provide them to end users that feel they need this level of measurement for themselves.
The calculations are pretty basic if you are into room acoustics. Look at the impulse response and determine if it is being affected by the room and how much. If the impulse times match the distances for reflections, then it coincides with the room, if not, then you need to look elsewhere. The real issue becomes is there something different going on with the time energy curves (this can be viewed in the waterfall plots as well) in the frequency you are describing as a problem, vs the rest of the frequency spectrum. As Sherlock Holmes--I would look for these differences--in all areas of measurement (not just the ETC and waterfall) and then try to logically deduce why they exist and how they might effect the overall performance. I do agree with you--it is a Sherlock Holmes exercise, because you have to go after what you first suspect--it may lead you to nothing, in which case you have to look elsewhere--thus I have not provided a solution--just some areas to look into further. |
Yeah, Judith -- I think you may need to test the analog waters. One pretty simple way you can rule out room interactions is to listen to the music via a decent pair of headphones. Heck, even a cheap pair of Grado SR 60's will tell you what you want to know. If the piano still sounds a bit odd through competent headphones, then you will know it's your source (especially if you use the CD player's headphone jack, if one is present).
Of the three sources I use for reference, I'd have to say my least expensive source (Teac X-700R reel to reel recorder) sounds the most natural and true to the music. This would be followed closely by my Michell turntable and my CD playback system in that order. The old reel to reel exhibits the most background noise (sans its noise reduction) but the timbre and harmonic structure is exceedingly true-to-life. The CD playback gear is dead quiet and very dynamic, yet compared to good analog, the authenticity of the various instruments is not quite "there". But it sounds close enough if one only listens to CDs, without a direct comparison to credible analog... Actually my digital gear does piano quite well since the latest DAC mods and the performance gap between my three sources is surprisingly narrow (yet clearcut). Also, the more resolution your system has, the more apparent/glaring any imperfections will be. |
Platos suggestion is a good one for testing the CD player. Whatever you do find, please do post it here--now I'm curious. |
So who's Dr Wattson over there? That depends I believe on all variables stated above + the AMPLIFIER that often may clip or increas the amount of distortions in 1000Hz piano notes. |
I could be wrong but i think speakers are at fault. Once i listened B@W 801, and had similar characteristics as Judit described. |
This thread turned out to be more fun then I would have deduced. It could also be that Judith's speakers have a crossover in the vicinity of the frequency band in question that may have some negative effects... |
Are these the same speakers/amp that you mentioned under a previous thread? In this thread you mentioned difficulties with orchestral brass... If so I suspect you may have a defective speaker or a poorly designed one. You really need go to a pair of QUAD ESL 63s, 988s, or Soundlabs. |
Ivanj, the speakers/amp are the very same mentioned in my orchestral brass question. I believe they are suspect here as well. A move to new speakers/amp is in my future. However, I want to be certain that I am actually treating the correct disease.
Plato, Relevant crossover is at 3 KHz. Your idea is the very first one I checked out.
I put a heavy quilt over my head and one speaker, listened to very near field direct path. Problem is audible. So I am thinking the room is not my problem.
I am going to do some equipment swapping tomorrow.
Some interesting ideas provided here. Thanks. |
Marakenetz, What does amplifier clipping sound like. I know what it looks like on paper, but don't know what it sounds like. Shouldn't clipping artifacts go away at reduced volume levels? |
Judit,
In my experience, clipping sounds like the ch in challa or chutzpa at both the top and bottom ends as the amp begins to clip. Increasing the volume decreases the intelligent audible spectrum as the distortion starts from the outside edges towards the middle.
The distortion caused by clipping does disappear when the gain is decreased. |
Frankly, if the phase angle and impedence is brutal at the frequencies you are mentioning the amp would actually only be putting out a fraction of its "FTC" output. An example would be a 200 wpc SS amp - into 8 ohms - which actually is only putting out 6 watts or so at this nexus. Thus clipping occurs even though the volume is low. (This is why, in part, so many of the 70s SS amps of high power did not drive real speakers as well as a 35 watt Dynaco tube amp.) Am I being clear? |
Sherlock Holmes has spotted Dr. Moriarty ... Today I took 7 piano CDs to an audio store and listened to an entirely different system than my own - Magnepan 3.6, Levinson CDP and pre, and Audio Research tube amps.
I must tell you how surprised I was to find that this system had exactly the same problem with piano that I was hearing in my own listening room. This has convinced me that Plato may have hit the nail on the head. Digital playback is where Dr. Moriarty hides. Either there or in my ears.
The problem with brass playback I am having, appears to be unrelated, as it did not occur during today's listening session. |
Hmm...lots of midrange drivers (esp 5") have a rising frequency response between 300 and 1k or so, which will thin out a piano,sometimes with a "cuppiness" coloration on human voice, too. For that reason I've preferred 6.5" midranges as a rule for inexpensive speakers. I've designed both 5" and 6.5" two-ways, and have a Steinway B in my room as a reference, and could NEVER get the 5" to sound as neutral as the 6.5. (Yet a GREAT 5" CAN be made to sound neutral, of course, as was accomplished Verity Audio in their Parsifal Encores, for example). Also note that room reflections around 800-1k are VERY position sensitive. Try moving your listening position just a few inches to see if the mids even out. That may tell you to play around with sidewall-damping schemes like sofas/pillows (what I use), etc. I do NOT buy the CDP suggestion as the source. There are other issues ("digititis", etc.) with CDPs, but a rising frequency response in the midrange isn't one of them!
Good luck. |
Judit-
Could you please list the CDs that show this phenomenon? I'd like to try it on my system and report back. Perhaps you could describe where, timewise/trackwise, the phenomenon occurs?
Thanks,
IJ |
IJ,
Several recordings which are pretty common members of people's libraries are
Nojima Plays Liszt, 1987 Reference Recordings
If you have this try track 2 La Campanella. I identified two spots where I think this is pretty pronounced; from 45-55 secs then from 1:30-1:45 seconds. However, the problem is sprinkled throughout this track.
Even more common in everyone's library is Patricia Barber NightClub, Track 1, bye-bye blackbird, during the long stretch of piano solo - listen to the segment from 2:35-2:48.
Another example: the Earwitness Transcriptions distributed by Madrigal Labs. Steinway Reproducing Piano. Disc one, track one Padereski plays Paderewski: Caprice Op.14 No.3 in G. Listen to the piano trills between 12-14 secs. The trills above and below these in frequency a bit further on are all clean and natural. However the trills between 12-14 seconds make my teeth resonate.
All three of these discs presented the same unpleasantness on the two entirely different systems that I listened to. Perhaps the one thread that tied these two systems together is that they retail for about the same amount of money.
Judith |
Subaruguru, glad you spoke up here since I know you have the same CDP I do.
The Nautilus 805s have a 6.5 inch Kevlar mid-range driver. Note that the phenomenon I am referring to occurred on the Magnepan 3.6 as well, in a totally different room driven by different electronics.
I moved my speakers around quite a bit to no avail.
I do not mean to spend people out on this problem, but I do appreciate the interest.
|
Judit, clipping of the amps usually makes drivers to produce "farting" sounds.
Exuse my friench:^) |
Not enough information, that's my diagnosis, Watson!
Since I don't happen to have the CDs you mentioned, can't do
a comparison. It could be just about anything. The first
thing to consider is two identical components that are in both systems that you listened to.
Or, that the pianos recorded happen to have this particularity?
Try some ESL headphones for a good listen?
_-_- |
