Topic: Test Signal Generator (Read 3478 times)

negopus · « **on:** June 21, 2004, 10:47:15 am »

In order to use Media Center as a measurement tool for the home audio setup, an audio generator (sine/sweep/white noise/coloured noise) could be added.

negopus

DocLotus · « **Reply #1 on:** June 21, 2004, 11:47:46 am »

Yes, that would be nice.

White noise & pink noise generation would be required.

Then with a good microphone, one could use the stereo visualizations to see how well your sound system is performing.

There would have to also be horizontal grid lines added to the stereo visualizations marked off in DB in order to tell the response curve of you sound system (speakers).

This seems like a doable thing & would add yet another neat new feature to MC11.

Would love to see this.

Matt · « **Reply #2 on:** June 21, 2004, 11:50:59 am »

Media Editor does this.

negopus · « **Reply #3 on:** June 21, 2004, 11:57:02 am »

Quote from: DocLotus on June 21, 2004, 11:47:46 am

Then with a good microphone, one could use the stereo visualizations to see how well your sound system is performing.

A really good microphone (and good preamp) is outside the price range of an amateur.
I have dynamic Shure's, they are robust but surely cannot be used for measurement.

BTW, I am looking for a cheap SPL meter, but they all start measuring from 50 dB. Quite insensitive. I would measure "silence" instead.

Quote

There would have to also be horizontal grid lines added to the stereo visualizations marked off in DB in order to tell the response curve of you sound system (speakers).

This is another feature I requested for visualizations. In general, a more "technical" view of audio would be good.

negopus · « **Reply #4 on:** June 21, 2004, 11:58:28 am »

Quote from: Matt on June 21, 2004, 11:50:59 am

Media Editor does this.

Does what? Test signal generation or displaying of grids?

DocLotus · « **Reply #5 on:** June 21, 2004, 01:01:30 pm »

Yes, me too

Does what ?

I have never seen these things in MC.

Where are they ?

DocLotus · « **Reply #6 on:** June 21, 2004, 01:07:35 pm »

"A really good microphone (and good preamp) is outside the price range of an amateur. I have dynamic Shure's, they are robust but surely cannot be used for measurement."

Very true, but one can get a relative measurement, make changes with the equalizer & see the affect if the change until the system sounds "right".

lee269 · « **Reply #7 on:** June 21, 2004, 01:17:08 pm »

Quote

I have never seen these things in MC.

This measurement stuff is over my head, but...

In MC: Tools/Advanced tools/Media Editor

In Media Editor: Create a new file, choose the Generate menu.

lalittle · « **Reply #8 on:** June 21, 2004, 03:20:30 pm »

Quote

A really good microphone (and good preamp) is outside the price range of an amateur.

This isn't really the case these days. Behringer offers the ECM8000 calibration microphone for about $40, and their smallest UB series mixers -- which have very flat, very quite mic preamps -- are around $50. While the ECM8000 might not be quite as flat as esoterically priced units, it's still plenty flat for typical measurement/calibration purposes, and is commonly used with software real time analyzers like TrueRTA.

If you want more accuracy from this mic, you can have the mic's response measured and a compensation file created. Using this mic calibration file will result in extremely accurate measurements.

Larry

DocLotus · « **Reply #9 on:** June 21, 2004, 06:41:14 pm »

+- 1 or 2 db is usually good enough for speaker setup.

negopus · « **Reply #10 on:** June 23, 2004, 01:09:08 pm »

Quote from: lalittle on June 21, 2004, 03:20:30 pm

Behringer offers the ECM8000 calibration microphone for about $40 [...]

I wasn't aware of that. Thanks, I'll take a look.

Quote

If you want more accuracy from this mic, you can have the mic's response measured and a compensation file created. Using this mic calibration file will result in extremely accurate measurements.

There is a plugin that does just that "reverse equalization": Antares Microphone Modeler (http://www.antarestech.com/products/amm.html)

negopus · « **Reply #11 on:** June 23, 2004, 01:50:39 pm »

Quote from: DocLotus on June 21, 2004, 06:41:14 pm

+- 1 or 2 db is usually good enough for speaker setup.

Do you know of an acceptable setup to measure PC noise (and its spectrum)?

DocLotus · « **Reply #12 on:** June 23, 2004, 02:20:35 pm »

Acceptable setup meaning reasonably priced ?

No; was hoping that would be added to MC.

When I worked for GE I had access to everything that I needed...
* Clean signal generator for linear, white & pink noise generation.
* Calibrated microphones with known linearity.
* Very high-end Spectrum analyzers.
* Oscilloscopes.

Was able to produce pink noise of +- 0.30 db... very good for system & speaker test.

This could all be done with software in MC if JRiver decided to add these features.

DocLotus · « **Reply #13 on:** June 23, 2004, 02:34:08 pm »

You ask and you will receive.

Was just playing around with lee269 suggestion off...

Tools/Advanced tools/Media Editor

It already does White & Pink noise generation; wonderful, simply wonderful.

Question to Matt... what is the accuracy of the white & pink noise generation in db ? How flat are they ?

Now if MC can do the other half of the test and read the results from a calibrated microphone then we have most of what is needed to test speaker (and system) linearity.

negopus · « **Reply #14 on:** June 23, 2004, 03:04:03 pm »

Let me clarify what I mean by accetable.

Commercial SPL meters (such as Radio Shack's) have a minimum sensitivity of 50 dB. Since a reasonable quiet PC produced 30 dB of noise or less, such meters are therefore useless. Accetbale, in this case, means sensitive.

I know that any mic preamp can boost by signal 60 dB but, unlike music and voice recording, you have to keep an eye on absoulte reference levels. So you have to keep control of the entire audio chain, knowing the gain of each component.

Price is always important, of course.

DocLotus · « **Reply #15 on:** June 23, 2004, 03:20:51 pm »

You need a General Radio or other commercial sound level meter for really low noise floors. The ones we used at GE went to 30db or lower.

Outside of an anechoic chamber, there are very few places lower then 30db (very quiet).

Most PC's are much louder than that if they have any fans in them.

negopus · « **Reply #16 on:** June 23, 2004, 03:45:55 pm »

I am interested in associating the perceived level with an absoulte value.

Can General Radio be found in Italy?

DocLotus · « **Reply #17 on:** June 23, 2004, 03:57:34 pm »

General Radio or GenRad as they became known was acquired by another company. I did a Google search and found several hits for GR equipment (mostly used).

They were a world wide company when I was at GE, but that was awhile ago.

Suggest you do a Google search for sound level meters or spectrum analyzers.

negopus · « **Reply #18 on:** June 24, 2004, 01:44:23 pm »

Here is what I found about measurement instrumentation:

General Radio (GenRad) has been sold to IET Labs http://www.ietlabs.com/index.html and Teradyne http://www.teradyne.com/. IET Labs still sells GenRad meters:
GenRad 1565: Sound Level Meter (40-140 dB; ANSI type 2; A, B, C weighting)
GenRad 1982: Precision Sound Level Meter and Analyzer

A complete history can be found at http://members.cox.net/dalehcook/radios/pages/gr.shtml

Behringer http://www.behringer.com/ makes a measurement microphone, ECM8000 http://www.behringer.com/ECM8000/index.cfm?lang=ENG, whose MSRP of about 60$ (or 60 Euros).

DocLotus · « **Reply #19 on:** June 24, 2004, 02:48:45 pm »

Yes, I had seen most of that.

Another great brand is B&K (Brüel & Kjær), they make very high quality sound level meters. Might be a bit on the expensive side though.

negopus · « **Reply #20 on:** June 27, 2004, 11:50:01 am »

Yes, Brüel & Kjær has a sound meter line too (http://www.bkhome.com/bk_template1.asp?spid=210&ctid=6). I did't find their prices yet, so I'm still here writing.

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Author Topic: Test Signal Generator (Read 3478 times)