MLS measurement with Speaker Workshop and Creative USB sound card: not working - diyAudio
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Old 2nd August 2005, 08:04 AM   #1
tcpip is offline tcpip  India
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Unhappy MLS measurement with Speaker Workshop and Creative USB sound card: not working

I've bitten the bullet, after more than a year of guidance from seniors at DIYaudio and Gooroo Angshoo. I've decided to learn how to use a software program to measure driver parameters, optimise a passive xo, and design my own speakers. And as expected, I'm stuck pretty early in the process.

I'm using MS Windows XP Home and Speaker Workshop on a 2GHz laptop. My sound card is the Creative Digital Music MP3+ USB. It has RCA line ins, RCA line outs, plus a mono mic in (with phantom power) and headphones out. It works in full duplex.

I've built a loop cable, and tested it with a DMM to ensure that the signal from the left lineout actually is directly connected to the line ins (left and right). I've read the Unofficial Speaker Workshop Manual v1.0 (first part on calibration and config), and I've successfully done a "Record" through Speaker Workshop with sine waves. When I do a "Loop Record" and play with the mixer's volume settings, I get to set the amplitude correctly such that there's no clipping. See the screen shot here:

Click the image to open in full size.

Therefore I'm certain that my loop cable is working, and also that Speaker Workshop works smoothly with my sound card to play and record signals. When I try to do a "Record" using MLS, I get a strange graph:

Click the image to open in full size.

As you can see in the bottom left of the image, the VU meter is showing very large amplitude signals. (I subsequently cut the volume in the mixer and got the MLS signal to stay within reasonable limits --- i.e. no clipping.) However, I can't see any trace of the signal in the graph. Where is the signal? What am I doing wrong?

And when I try to use the impedance jig to measure a test resistor, it doesn't give me any reading at all.... it just shows me no reading, i.e. zero impedance.

Angshu told me to try changing the latency settings. I've tried all latencies from -20 to +20 or so. No luck.

If the VU meter is reporting high amplitude signals, why can't I see it in the graph? I thought perhaps the high-amplitude pulse is to the left of the origin of the graph, so I changed the min-max range of the X-axis in "Chart Properties" to start the graph from -20msec onwards. I thought zooming in to a small part in the beginning of the time period would help, so I changed the range (X-axis) from -20ms to +50ms. I also switched off all vertical grid lines and tick marks, so that no pulse of the graph would be hidden behind these lines. No luck. The graph is absolutely devoid of any pulses other than that tiny one after about 20ms.

Please help.
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Old 2nd August 2005, 10:04 AM   #2
jomor is offline jomor  Greece
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open the Recording Mixer of your sound card and enable the viewing of all available potentiometers. If you see a potentiometer named "What you hear" (or something like that) do enable it and try to do an mls signal recording. On some sound cards that have the additional "What you hear" potentiometer, you need to switch to that option for mls recording, while it works with the Line-In for sine recording.

Speaker Workshop is a bit confusing at first, but when you manage to do proper calibrating and settings, it gives very accurate results. Its our best friend for crossover design! and its free !

( do visit Claudio's website, its really heplful to start fast with speaker workshop step by step in an easy way http://paginas.terra.com.br/educacao...negro/english/ )
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Old 2nd August 2005, 10:39 AM   #3
tcpip is offline tcpip  India
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Default No "What you hear" with the SB DM

Quote:
Originally posted by jomor
open the Recording Mixer of your sound card and enable the viewing of all available potentiometers. If you see a potentiometer named "What you hear" (or something like that) do enable it...
There's no such potentiometer on this SB Digital Music MP3+

Quote:
( do visit Claudio's website, its really heplful to start fast with speaker workshop step by step in an easy way http://paginas.terra.com.br/educacao...negro/english/ )
Yes, I've seen it, and it's really helpful. However, the problem I'm facing appears very specific and till I lick it, the other guides and manuals won't help, I think.

Thanks for your suggestions.
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Old 2nd August 2005, 12:45 PM   #4
jomor is offline jomor  Greece
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ehm, check the volume control mixer too if you already haven't done so. you could also post a thread at the speakerworkshop forum, if i m not mistaken there are some members there who have the same soundcard with you and perhaps someone could have faced the same problem
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Old 2nd August 2005, 02:58 PM   #5
tcpip is offline tcpip  India
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Quote:
Originally posted by jomor
ehm, check the volume control mixer too if you already haven't done so. you could also post a thread at the speakerworkshop forum, if i m not mistaken there are some members there who have the same soundcard with you and perhaps someone could have faced the same problem
What should I check on the volume control of the mixer? It's set to a value where it doesn't clip. Should I set it lower? And yes, I think I should try the SW forum... that may get me more specific help.

Thanks.
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Old 2nd August 2005, 03:21 PM   #6
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If your creative card is anything like my Audigy II ZS then there are a few important things you need to do to get it to work.

You must choose the Analog Mix as your recording source, and in the control panel (ie system one) sound settings you must go to the recording control panel, and click on the advanced button for analog mix, and tick the record without monitoring tick box.

also do not mute the line in control ( I think the unofficial speaker workshop manual says to do this).

see screen print.

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Old 2nd August 2005, 03:27 PM   #7
kan3 is offline kan3  United States
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Is MLS measurement the only thing your using speaker workshop for?

Is so then try these free and easy to use alternatives:

http://www.wavecapture.com/DOWNLOAD/LL3/LspLAB3Demo.exe

http://sourceforge.net/project/showf...ease_id=302959
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Old 2nd August 2005, 05:40 PM   #8
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If you will notice in your first chart, the sinewave doesn't start untill about 24mSec. This is called LATENCY and indicates a delay between the time the signal is generated, then received and processed by your sound card.
If you notice your second chart, it only displays to about 10mSec...therefore you are probably not even seeing the data. Actually, with latency this high it may not even make a measurement correctl at all. Try changing the second chart's properties so that the X AXIS extends out to 40mSec like the first chart.

Also, you will need to correct for this 24mSec delay before you can get good measurements. Here is a quote from the SW Help File:

"Debug tab (Options Preferences dialog)

This tab contains system specific settings. There is a checkbox to let you enter debugging mode (don’t use this unless asked to by Audua personnel), and there is a data entry field to set the Latency value.

Latency:

When Speaker Workshop performs a record operation it synchronizes the input and output signals using capabilities of Windows. This synchronization could be slightly off, depending on the speed of your computer and sound hardware. Set this value to adjust the synchronization to compensate for those effects. A value of 0 uses the standard synchronization. Non-zero values adjust the synch point forward and backward in milliseconds.

To set the value: perform a signal record operation using an MLS signal in loopback mode (just because an MLS is easy to see) and look at the recorded signal. The MLS should start at the left edge of the chart. Expand the left edge to examine the signal closely. If the signal starts before the chart begins (valid data is visible at time 0) you should try shifting the latency using negative values, perhaps –5 to start. If there is blank space and then the signal starts you should adjust the latency forward by the millisecond delay you want to introduce. A delay of <5ms is adequate and will work fine with Speaker Workshop, although you might want to tweak the delay to less than 2ms for slightly better noise results. Perform this operation a few times to make sure your computer system is consistent – the delay doesn’t vary.

Latency is stored in the system registry and will be used for all record operations, including measurements, and with all databases.

MLS Warm up
The sound card you use may very well have startup issues when starting a record operation due to things like capacitors charging up and clocks getting to speed. As an option, Speaker Workshop lets you send a short low-level signal to the card before the actual data is sent. This seriously improves the measurement quality for a single sample and marginally improves multi-sample tests as well. The default of 100 seems to work well. A longer default would help with a card that takes a long time to get to full performance. This can be checked by doing a simple Measure Impedance of a driver with a single MLS sample with different warmup settings."


Ironically, SW actually works better with older PC's...the newer sound cards seem to have much more latency than the old ones, as well as a lot of un-needed software and drivers which cause problems with SpeakerWorkshop. The program was developed back in the day "SoundBlaster 16" cards were common.

Also, there may be some help at the SW soundcard thread:
http://www.speakerworkshop.com/forum...opic.php?t=925
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Old 2nd August 2005, 07:14 PM   #9
tcpip is offline tcpip  India
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Quote:
Originally posted by wintermute
If your creative card is anything like my Audigy II ZS then there are a few important things you need to do to get it to work.
Actually, my sound card is a very simple stereo-in, stereo-out card, and doesn't have the Analog Mix source. Also, I can't afford to keep the line-in muted... that's the only input I'm using.

But thanks for the pointers.

Quote:
Originally posted by kan3
Is MLS measurement the only thing your using speaker workshop for?
Thanks for the pointers. I'll try the first of the two links you gave me --- the other one seems to be too raw: v0.0.1

BTW, will RightMark AA also do such measurements? And I'm using --- or intend to use --- SW for the full speaker designing process, not just MLS measurements. SW is currently the only speaker design software I have, including xo design, box design, and measurements.

BTW, I seem to find that SW's vented box design module does not support SBB4 alignment. Is this correct? I think I saw only BB4 and QB3 and one other alignment. Why is SBB4 not included? Just curious.
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Old 2nd August 2005, 07:26 PM   #10
tcpip is offline tcpip  India
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Quote:
Originally posted by jbateman
If you will notice in your first chart, the sinewave doesn't start untill about 24mSec. This is called LATENCY and indicates a delay between the time the signal is generated, then received and processed by your sound card...
Thanks for the patient and detailed reply.

I too had read those portions of the Unofficial SW Manual, and I had sort of guessed that the part about latency controlled what you've mentioned. Just to be sure, I took some fresh recordings with the loop cable, both sine wave, once with the latency set to zero and the next time with latency set to 20ms. Here are the two graphs, and it's very clear that setting the latency to a positive value shifts the entire signal to the left, as you'd explained:

Click the image to open in full size.

The image above had latency = zero. The one below has latency = 20ms.

Click the image to open in full size.

Quote:
If you notice your second chart, it only displays to about 10mSec...therefore you are probably not even seeing the data. Actually, with latency this high it may not even make a measurement correctl at all. Try changing the second chart's properties so that the X AXIS extends out to 40mSec like the first chart.
After reading your comments, I took some fresh MLS readings, and the graph of the signal remained completely blank, as I'd feared. As you can see now, the X axis extends well beyond the latency point. AND these MLS readings were taken with the latency setting set to 20ms, which means if there was anything in the graph, it would shift left by 20ms.

The first graph below shows the amplitude against time for the MLS recording, with latency set to 20ms:

Click the image to open in full size.

And this one is the FFT of the earlier graph:
Click the image to open in full size.
In this one, you can clearly see the frequency peak at 1KHz... I presume the MLS signal has a 1KHz frequency.

Quote:
Also, you will need to correct for this 24mSec delay before you can get good measurements.
As you can see, I did the correction and it has amounted to nothing. In fact, if you read the very first posting in this thread, I'd mentioned that I've played around with the latency setting, trying everything from -20ms to +20ms. Didn't help. However, there's certainly some high-amplitude signal somewhere, otherwise the VU meter wouldn't have shown such a magnitude.

Quote:
Ironically, SW actually works better with older PC's...the newer sound cards seem to have much more latency than the old ones, as well as a lot of un-needed software and drivers which cause problems with SpeakerWorkshop....
I sincerely hope this won't be a show stopper.
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