MY DL NOISE ANALYSIS

[WK154]

In a recent effort by iBloke to solve his DL Noise problem he kindly  provided me with a 30 second sample of the offending noise produced by the DL. I analyzed it with hopes that it would lead to narrowing the source of the problem. On 7/15/14 I also informed Ben Olswang at Mackie and sent him the sound file for analysis by his engineers in hope that they would be able to provide their insight since they are in possession of information relevant to this that I don't have access to (schematics, PCB layout and code for starters). So this assessment is based on what I do have and past experience in the field. Here is the e-mail:

E-mail send on 7/15/14
Hi Ben,
I recently received a recording of the noise exhibited by the DL. After
analyzing it I have some theories regarding the source. I'm hoping that you can
let your engineers comment on this. Would like as quick a turnaround that you
can muster before I post. Attached is the noise file for your information. It
appears that a high frequency content in the 12k-15k range is contained in 4
lower frequency cyclic envelopes (possible ringing). It may be limit cycle
oscillations that could be from the D/A converters. When I autopsied the DL a
year ago I was only interested in the under the hood power and did not pay
attention to much else. After reading the Spec on the AKM D/A I noted quite a
few cautions by them on unterminated inputs and certainly layout concerns
regarding analog and digital ground planes. I looked at the pics and found no
evidence of separate grounds in the DL. This may also be the reason for the poor
pin one results. Since I have neither the schematics nor the PCB layout it's
clearly a guess based on my experience. I hope Mackie can shed some light on
this problem ASAP, a fix of course would be better.
Bill
It is now 10 days later 7/25/14 with no response as of this post to the requested subject from Engineering. Ben has communicated several times since and I appreciate his efforts. I don't know what internal hurdles stand in his way off course.
For those that don't know what my autopsy Pics where here is a link showing the main board.
https://www.dropbox.com/s/vly1hfnu0m4ulht/Dl1608%20Mobo.JPG
You will see some of the analog section at the top by all the cables and the D/A converter chip (medium size chip) at the far left. It's one of five required the other four are in the analog/power supply section that I didn't take apart. The rest are NJR4580 OP amps and the A/D converters. The power supply connector enters from the bottom and is certainly another poor design practice. Take a page from the PC board designers and ALL power connectors get as close as possible to the on-board power converters as possible. The ARM and DSP are supplied with similar converters but half the board away from the power connector. A source of lots of switching noise and yes the D/A is next to the converters, really!! There appears to be a ground plane wrapping the top and some of the side but no clear delineation or evidence of separate ground planes (analog and digital) based on the visual. Can this problem be solved without a redesign? Probably since it's borderline. With better control of the D/A converters via software this can be minimized. Certainly don't feed the D/A bad data. It's also not white noise, pink noise, it's just narrow band high frequency noise (12-15kHz). The Sync problem is separate from the noise as has been proven by many. Enough of this I am short on time and patience. The ball is in Mackie's court and requires a fix so we can all move on. For now I would not recommend this mixer.

[abzurd]

Not sure how or even if this ties into the noise issue you looked into but here's a yet to be seen in public video that I sent to Mackie several months ago. It shows 2 issues. The first is distorted sound at 1/2 volume then is the dreaded "blast".


It loses clean audio at 1:47. You can hear the audio drop dramatically and some distortion over top of it. Eventually the blast of noise comes and goes. This is what happens about 25% of the time. 75% of the time it goes straight to the blast of noise at very high volume. I also have a sync video I sent them.




Anyway, for those not experiencing the noise, here it is for all to hear.

[WK154]

Thanks for the info. It's 3 short bursts with a range of 90-300Hz but no high frequency components that iBloke's audio contained. A very different source possibly from the player. The iPad had sufficient control to get music back, not at all the case with iBloke's.

[WK154]

There is only one way to get to the bottom of this and that is to get units that are failing in this mode. No amount of surveys will help, that's just a time waster or other marketing maneuver. How else would you know if you try a solution to see if it's fixed, especially if it's software based.

[mtsens1]

Not sure how or even if this ties into the noise issue you looked into but here's a yet to be seen in public video that I sent to Mackie several months ago. It shows 2 issues. The first is distorted sound at 1/2 volume then is the dreaded "blast".


It loses clean audio at 1:47. You can hear the audio drop dramatically and some distortion over top of it. Eventually the blast of noise comes and goes. This is what happens about 25% of the time. 75% of the time it goes straight to the blast of noise at very high volume. I also have a sync video I sent them.



Anyway, for those not experiencing the noise, here it is for all to hear.

I'm curious as to why in the failing state, the volume loss and noise seem to be a result of the app playing the music, but when you switched to the iTunes app it played music fine, while apparently the other app was still sending garbage? To me this wouldn't indicate a iPad or mixer issue. From the video, I would assume the app is the issue. Thoughts?

[abzurd]

Not sure how or even if this ties into the noise issue you looked into but here's a yet to be seen in public video that I sent to Mackie several months ago. It shows 2 issues. The first is distorted sound at 1/2 volume then is the dreaded "blast".


It loses clean audio at 1:47. You can hear the audio drop dramatically and some distortion over top of it. Eventually the blast of noise comes and goes. This is what happens about 25% of the time. 75% of the time it goes straight to the blast of noise at very high volume. I also have a sync video I sent them.



Anyway, for those not experiencing the noise, here it is for all to hear.

I'm curious as to why in the failing state, the volume loss and noise seem to be a result of the app playing the music, but when you switched to the iTunes app it played music fine, while apparently the other app was still sending garbage? To me this wouldn't indicate a iPad or mixer issue. From the video, I would assume the app is the issue. Thoughts?

This was just one example. It would blast the noise with the native music player as well as another music player I tested. The mixer just never liked that ipad. It often refused to sync. I used to have to "jump start" the mixer by docking my original ipad then switching it with the Ipad3. That became the only way I could dock the thing at all. The noise issues didn't appear until iOS7, but the disconnect issues were always an issue, though much worse with iOS7.