Great replacement for O scope to set gain structure? - Page 2

That's not an accuracy issue

For some reason brucek believed that the bit rate of the BFD’s A/D converters was a function of signal level, and that lower signal levels resulting from switching the BFD’s operating range to the high would make it functionally a lower bit rate device, and therefore noisy. He surmised that even though the BFD is a 24-bit device and should be capable of delivering a dynamic range of 147 dB, its background noise spec of 94 dBU (unweighted) meant that it actually had barely 15 bits of resolution. So with only 15 bits available to define input signal levels, he felt that it was imperative to supply it with the maximum possible signal strength.

This simply isn’t true. His first mistake was believing there was a relation between the BFD’s noise spec and the bit rate of its A/D converters. There are all kinds of things that determine a component’s noise level besides just the converters, and indeed its factual noise level has no bearing on the bit rate of its A/D converters. For example, the why is the 24-bit BFD known to be a noisy equalizer, while the Yamaha YDP2006 is dead silent with a mere 20 bits?

The second mistake was not recognizing that the quantization of modern 24-bit converters is so robust that it makes them virtually impervious to degradation from low signal levels.

Regards,
Wayne A. Pflughaupt

Thank you for the advise.
My question was probably premature. I have not spend enough time tweaking things to tell if this is gong to be a problem.

The signal chain is Denon 4311 sub out to inuke nu3000DSP.
To my emberrasment i just discovered that my Audyssey guided gain settings are way off. I tried to obey Audyssey recommendation for keeping sub SPL close to 75dB during calibration which I did by adjusting the volume control on the amp. My "calibrated" sub output level on the AVR is -7. However with this setting I am far away from reaching max power level on the amp. I was trying to get the amp into clipping theritory watching WoW at "reference" the other day. I had to bump sub level on the AVR to 0 and increase input gain on the amp by 7 dB to get the limiter lights turn on.
My plan for now is to set the gain per Ricci and ignore audyssey warnings during calibration. If I end up with the sub output trimmed all the the way, I may follow your adsvise and adjust settings of other channels.

Clipped and unclipped.

James

60HZ clip measurements.BMP 150k .BMP file 60HZ no clip measuremnets.BMP 150k .BMP file

autox,

To be honest I am not sure what the latest firmware is right now, I updated mine when I used it for setting my gains and have not used it since. I believe the seed studio forum would have the latest firmware. If I am not mistaken the manual states how to deal with the SD card for the unit.

James

Well using my original suggestion of REW and something to attenuate to correct levels, you have about a $20 cost and considerably better accuracy, plus you can see the spectrum to help diagnose faults, and the noise floor which is a major advantage, rather than a binary good/not good which does nothing to help determine SNR.
Edited by A9X-308 - 2/11/13 at 10:59pm

Here's the example I liked the most of the source sig and a sample of THD with the DD-1

https://www.youtube.com/watch?v=E7lZ5ULUil8

Yup...Poor mans solution.


BTW...I attached an article on gain structure from Community sound. This is one of the easier to understand examples of why and how to do gain structure that i have seen for the layman.

GAIN_ADV_TECH.pdf 111k .pdf file

By what mechanism would that happen, unless the 'scope itself is clipping?

Liked the article, thanks for sharing. Saved. Especially the easy to see bar graph to visually comprehend how it can be thought of. I've always viewed as a window of range and I liked seeing it worded that way.


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same concept
As with what was discussed with multiple amps (my back in the day car audio) "level" matched with a multi-meter. Same concepts. If say have 4 amps on multiple VC's or sharing enclosures. Each amp measures different AC voltage output for maximum potential. Using the one with the lowest output and back down others to match. Same concept with signal chain devices. Your always limited to the weak link device for the window.

When the article mentions complicating things with EQ etc, that's also referring to +/- levels(and any induced EQ) in the AVR for each channel. Let's say for subwoofer out Wayne's procedure says to max it out so then the volume raised shows maximum number before distortion/clipping. True but the subwoofer setting in the AVR might not be set at that level for the final preference setup which makes the overal volume of the AVR lower. And that setting effects the mains tied to the volume might not reach potential (especially if you have more outboard amps tied to them). I prefer using zero/flat settings in the AVR find max volume then adjusting each one individually to see if there's any trouble pre gain clipping or distortion.

To try and sum; our AVR (at max volume) sub setting is usually at (0 / +3) and can go to +6 before clipping the next device (BFD). At this same volume level for this setup the mains are also within clip range of their respected outboard amps. This way everything is tied and come up together within the max overall window. "edited" to add one thing I've noted is if your AVR channel settings are far from 0 like say +7 or something you can tell there's more main volume probably left of the table. If it's far in the minus like -7 you main volume is probably higher than it needs to be and hot.

Just a quick thought on using the sig gen in REW. I could be completely wrong but my thought process is the signal levels out of your sound card might not be the same as your true source ie dvd player or media pc card. I can see it working well if you have your main media pc running REW from it to setup.
Edited by autox320 - 2/12/13 at 8:12pm