nwavguy, thanks for contributing so helpfully and courteously on this issue. The points about measurement certainly fit my own experience of trying to measure sound levels.
I find this site useful for a lot of things, including the subjective assessments and the inventive vigor of its participants, and I would hope that we could welcome other work without being too defensive.
Anadtech has a nice db chart on today's large hds
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nwavguy: "If you look at my posts, I've NEVER suggested SPCR change their testing methodology."'
You didn't? What is this then: "Some similar reviews here on SPCR would only help things further."
To me, that appears like you'd welcome SPCR to join the ranks of all other review sites who use close mic technique already.
"Standing waves DO cause distortion, not just attenuation as you suggest. The cancellation happens only at some frequencies, not all frequencies equally."
Just a while ago you did say ALL instead of some... you also used ALLCAPS to emphasize the word all: "And there will be standing waves at virtually ALL frequencies causing lots of cancellation effects significantly distorting the measurement."
Well, you didn't bold and underline it...
"The simple fact is this: The closer you get the microphone to the noise source, the less inaccuracies you have due to cancellation and other outside influences."
And I never questioned that fact (that is, if I don't keep forgetting what I've typed like you do all the time). I was not talking about outside influences but more the influence of the object to be measured itself. Why are you so fixated about outside influence that you completely deny the meaning of distortion due to surface topography of the object itself?
"If you don't have an anechoic chamber, however, a close mic technique will likely provide the most accurate results."
But only up to 500 Hz... practically useless.
You didn't? What is this then: "Some similar reviews here on SPCR would only help things further."
To me, that appears like you'd welcome SPCR to join the ranks of all other review sites who use close mic technique already.
"Standing waves DO cause distortion, not just attenuation as you suggest. The cancellation happens only at some frequencies, not all frequencies equally."
Just a while ago you did say ALL instead of some... you also used ALLCAPS to emphasize the word all: "And there will be standing waves at virtually ALL frequencies causing lots of cancellation effects significantly distorting the measurement."
Well, you didn't bold and underline it...
"The simple fact is this: The closer you get the microphone to the noise source, the less inaccuracies you have due to cancellation and other outside influences."
And I never questioned that fact (that is, if I don't keep forgetting what I've typed like you do all the time). I was not talking about outside influences but more the influence of the object to be measured itself. Why are you so fixated about outside influence that you completely deny the meaning of distortion due to surface topography of the object itself?
"If you don't have an anechoic chamber, however, a close mic technique will likely provide the most accurate results."
But only up to 500 Hz... practically useless.
Just to clarify a few points for whiic... The only reason I've gone down the path of discussing nearfield measurements was your comment:
The comment about all frequencies was only meant to say across all frequencies. With the microphone close, you only need to worry about cancellation at higher frequencies. With the microphone further away cancellation can be present across all frequencies of interest. Not at every single frequency, of course, but all across the audio spectrum.
And I think you'd be surprised how much typical drive noise is concentrated under 2000 hz and even under 500hz. The higher frequencies are much weaker and MUCH easier to suppress or capture with damping in the PC case, etc. The lower frequencies are the ones that are conducted by and escape the PC enclosure and hence remain audible. Even the nasty "whine" of older drives wasn't all that high--perhaps 500hz - 1000hz.
If you believe the so called "surface effects" of using the close mic technique are more important than everything else, and invalidate it as a testing method, that's fine. Like I said, we have to agree to disagree. I won't continue to repeat myself.
As colin2 said above, I think it's best to welcome a variety of work on reducing PC noise. My main point all along has been to enourage just that and not wrongly dismiss the Andantech findings. My comment you quote about SPCR was just to say I welcome them to test the current crop of drives using whatever objective method they'd like.whiic wrote:I think Anandtech's measurements are not only low on informational value but they may be in fact misleading, thus we might be better of completely without them.
The comment about all frequencies was only meant to say across all frequencies. With the microphone close, you only need to worry about cancellation at higher frequencies. With the microphone further away cancellation can be present across all frequencies of interest. Not at every single frequency, of course, but all across the audio spectrum.
And I think you'd be surprised how much typical drive noise is concentrated under 2000 hz and even under 500hz. The higher frequencies are much weaker and MUCH easier to suppress or capture with damping in the PC case, etc. The lower frequencies are the ones that are conducted by and escape the PC enclosure and hence remain audible. Even the nasty "whine" of older drives wasn't all that high--perhaps 500hz - 1000hz.
If you believe the so called "surface effects" of using the close mic technique are more important than everything else, and invalidate it as a testing method, that's fine. Like I said, we have to agree to disagree. I won't continue to repeat myself.
"With the microphone close, you only need to worry about cancellation at higher frequencies. With the microphone further away cancellation can be present across all frequencies of interest."
You could take a couple of different measurement from slightly different locations but all from the same distance. That way the HDD would always be 1.000 meter away but the reflection would have changed, and the measurements could be averaged.
Sure, you could make many measurements using close mic method, but you'd need more than just two or three of these measurements. Because you are measuring at few millimeters you have to pretty much place the mic right on top of the noise source to catch the higher frequencies (even as "high" as 1500 Hz). That includes (but does not limit to) measuring noise at every single chip on the PCB to catch all noise emitted by the HDD. And since chip layout on the PCB are different between manufacturer to another, these results wouldn't be comparable. Of course there's a method of near fail-proof close mic recording: take a measurement from every single square centimeter on the surface of HDD and the average the results. Well, even then you couldn't compare different form factor HDDs against each other because smaller dimensions would mean that first canceled frequency would be around 3000 Hz instead of 2000 Hz. Not to mention how difficult and/or expensive it would be to take those hundred measurements per review sample.
Of course if you're satisfied with knowing the frequencies up to 500 Hz, you could take that single measurement and be happy with the result. I think it's fairly accurate to that point without taking multiple measurements.
"Even the nasty "whine" of older drives wasn't all that high--perhaps 500hz - 1000hz."
Maybe. I have not analyzed the noise spectrum produced by old drives. New HDDs don't have ball-bearings to produce that "grind" (a word that probably describes the noise better than "whine" since bearing noise isn't pure tone) but they still can make some real nasty whine. For example SPCR's sample of 7200.9 500GB had a very nasty spike somewhere around 1500-2000 Hz (a frequency range completely canceled out in near field recording):
http://www.silentpcreview.com/article283-page3.html
You could take a couple of different measurement from slightly different locations but all from the same distance. That way the HDD would always be 1.000 meter away but the reflection would have changed, and the measurements could be averaged.
Sure, you could make many measurements using close mic method, but you'd need more than just two or three of these measurements. Because you are measuring at few millimeters you have to pretty much place the mic right on top of the noise source to catch the higher frequencies (even as "high" as 1500 Hz). That includes (but does not limit to) measuring noise at every single chip on the PCB to catch all noise emitted by the HDD. And since chip layout on the PCB are different between manufacturer to another, these results wouldn't be comparable. Of course there's a method of near fail-proof close mic recording: take a measurement from every single square centimeter on the surface of HDD and the average the results. Well, even then you couldn't compare different form factor HDDs against each other because smaller dimensions would mean that first canceled frequency would be around 3000 Hz instead of 2000 Hz. Not to mention how difficult and/or expensive it would be to take those hundred measurements per review sample.
Of course if you're satisfied with knowing the frequencies up to 500 Hz, you could take that single measurement and be happy with the result. I think it's fairly accurate to that point without taking multiple measurements.
"Even the nasty "whine" of older drives wasn't all that high--perhaps 500hz - 1000hz."
Maybe. I have not analyzed the noise spectrum produced by old drives. New HDDs don't have ball-bearings to produce that "grind" (a word that probably describes the noise better than "whine" since bearing noise isn't pure tone) but they still can make some real nasty whine. For example SPCR's sample of 7200.9 500GB had a very nasty spike somewhere around 1500-2000 Hz (a frequency range completely canceled out in near field recording):
http://www.silentpcreview.com/article283-page3.html
Well I don't think so. I've done a small test based on latest SPCR recordings : T133 and WD5000KS.nwavguy wrote:Most of the idle noise coming from a HD is under 500hz while the seek noise is a bit higher but the very high frequency components are very low in level.
Files are opened in Audition 2.0, converted to 32-bit, +20dB amplified; then I keep a 5-second region from the no-AAM seek test. This region is then split into 4 frequency ranges using a sharp FFT filter. I then create a file where you first hear 5-sec 0-500Hz, then 5-sec 500-1000Hz, then 5-sec 1000-1500Hz, then 5-sec 1500-22050Hz. This 20-sec audio file is then converted back to 16-bit.
Please note that you'll need a fairly high-end audio system including a high-fidelity subwoofer to properly hear the 30-100Hz range; headphones or PC speakers won't reproduce low freqs to their full level.
http://files-upload.com/files/440689/abcdtest.rar
On T133-1ft-noAAMseek-ABCD.wav you clearly hear that the 1500-22050Hz range is the most disturbing to the human ear; 0-500Hz next. Similar results on WD5000KS-1ft-noAAMseek-ABCD.wav but disturbing levels are higher. Results on 1-meter SPCR recordings are similar but the ambient noise floor is proportionally higher.
Last year I've been doing many HDD noise recordings at home (some were published in this forum), comparing P120, T133, T166, WD5000KS, WD5000AAKS as well as older drives; after a few preliminar tests I decided to place my microphone at 60cm because at this distance, the recordings sounded natural, similar to what I heard when testing, and my testing room was quiet enough so that ambient noise didn't interfer.
It's clear to me that any close-mic recording technique (let's say, anything below 10cm distance) will give a very big boost in low freqs and will severely lower the 1500-22050Hz range, so that global dB/A values wouldn't give an accurate idea anymore.