So, in order to keep this from getting buried in its original thread ("Inside out (comb-filtering) Sound") I just posted the recordings from my 990, made using the FRONT and Zone 2 outputs. The files are available in 320 kbps mp3 as well as FLAC formats; you can download these at will. I personally can't hear a difference in these files between the FLAC and the 320 kbps mp3's, but I thought that I would post them in FLAC (which is fully lossless and can be reconstructed to its parent wav file) if anyone thought the issue might be attributable to the mp3 encoding process (it's not).

Also, to show (graphically) the comb-filtering, I have posted the .jpg files (that show the spectra observed for the front and zone 2 ouputs for STEREO, BYPASS, and UPSAMPLE modes) to my FTP site so that they can be downloaded.

However, I also know that listening to the files will make it obvious why I see this as an issue, and why I'd like to know if other users are experiencing this; as you compare the FRONT files (all of which have the comb-filtering issue) you will hear that the BYPASS and STEREO mode-derived recordings sound very much alike, but you will note a difference in timbre when you listen to the UPSAMPLE-derived version. Compare the Zone 2 outputs to one another and you'll see they basically are identical-sounding, and all are free of the comb-filtering observed in the front outputs. So...the 'good news' is that my whole-house feed doesn't suffer from this issue...but the 'bad news' is that the system in my main listening room does.

If you want to check whether or not your 990 is doing this, please revisit the thread ("Inside out sound") and if you still have questions, just email me (my address is in my profile); I can post some white noise files if you like / need, or I could send one via email.

Anyway, once you log on (credentials are below) you will see that there are three folders - one for each mode BYPASS, one for STEREO, and one for UPSAMPLE. Each houses the jpg's, mp3's and .flac files that document the issue. I have the data from the otehr modes that I tested, and I may post those should there be interest from the Readers.

If you are using an FTP client (Filezilla etc) then after you log on just drag and drop the files that you want. If you want to do this from a browser window, then here's the string that you will need (you may need to copy and past the whole string):

FTP://owners_990.immersifi.com:combfilter1@immersifi.com

For those using an FTP client, the log-on details are as follows:

Username: owners_990.immersifi.com
Password: combfilter1
Host: immersifi.com

Thanks for reading this, and I'm curious to hear comments from otehr 990 owners; I hope that it's just my unit...or (best case scenario) that this can be fixed in a firmware update.

Test Files Just Added:

On the FTP site mentioned above, I just added six files than can be used for diagnostics (for helping to identify this issue or for other things). You will find them in the folder test_files.

NOTE: I assume no responsibility for how these files are used. As with any test, if indeed you are going to use these files, always start with the gain (volume control) all the way down on the 990 (or other device) and GRADUALLY increase the gain (volume) once you know the file is playing.

The files are:

1) White Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.wav, 44.1 kHz, 16-bit)
2) Pink Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.wav, 44.1 kHz, 16-bit)

From these two files above, the following four files were derived:

3) White Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.flac)
4) Pink Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.flac)
5) White Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.mp3, 320 kbps)
6) Pink Noise, 20 Hz - 20 kHz, 2-channel, 300 seconds' duration (.mp3, 320 kbps)

Feel free to use these for your own use.

If you want to try and replicate what I did (in order to see if your 990 exhibits the same problem) then burn a CD with these tracks and connect your CD/DVD player's analog outputs to an analog input on your 990. I would suggest that you use the white noise file rather than the pink noise version simply because there is more high frequency energy present in that than the pink noise version.

If you have an mp3 player handy, copy whatever format you prefer to use (.wav, .flac, or .mp3) and use a 1/8" to RCA male adapter cable and plug that into an analog input.

If your 990 exhibits the same problem as does mine, you will hear it right away when the analog source (to which your CD player or mp3 player is connected) is selected. Cycle through the various modes (STEREO, BYPASS, UPSAMPLE, DOLBY, DTS etc) and listen.

If you have a zone 2 feed, my guess is that you will not hear the comb-filtering in zone 2 - at least this is what's happening in mine.

Mark

Maybe Outlaw will check it out for you. Any news from them on your ticket? I am still about a week away from my 990 and may not have internet when I am there. I do have a lot of FM channels that can provide the white noise.

No news from Outlaw on the ticket. I'm definitely interested in your results - remember when you asked what comb-filtering would sound like? Well, just download the files...and you'll know first hand.

It's funny - I think I may have actually purchased my unit in the first lot - I think I filled out a form to be on the proverbial waiting list when the 990 was announced...and I remember, upon receipt, noticing the comb-filtering (on FM) simply because it was my only analog source at the time. The thing is...I did log a ticket then, so I think Scott et al could check the records and verify that the unit had an issue from day 1 (or appears to have an issue from day 1 based on comments I have received from another 990 user - he's put his through the paces, listened to the recordings that I made (having downloaded them from the FTP site), and says his 990 does not exhibit the problem with analog sources). Good news for him...bad news for me.

It also sounds like Outlaw is rather busy with the release of the new processor - at least this is what I have been told (that and 'due to the age of the unit' it would be some time before I heard back from them). I just hope that a) my unit has a hard fault and outlaw will exchange it (again, a B-stock unit would be fine), or b) this is indeed a firmware issue that (perhaps) only affects certain revision level boards / architecture. I would be more than OK with a firmware update...but if it turns out that I am just stuck with it (due to it being an 'old' unit), then I will be very, very disappointed.

I can't look-up the ticket (when I first logged the issue with what I thought was the tuner, but in fact has more to do with the analog signals than it does the tuner per se), because I submitted it as 'old_school' (at least, I think that's the user name I used) and since then I lost my password (which is why I now post as "old_school_2"), but indeed, I remember hearing the issue then.

Frankly, I think I may have more analysis tools at my disposal than do the folks at Outlaw (that's not a slam, it's just a statement of fact), so I'm not sure what they could find - apart from what appears to be the issue, namely, a hardware issue.

There is one other test that I need to run - not so much to see if the comb-filtering goes away, but to see if changing the delay settings changes the comb-filtering characteristics (something that another owner discussed with me earlier today). I will try to run those tests in the next few days and see if that is part of the issue with my 990.

[ADDED: I tried changing the DELAY settings (i.e. speaker distance) to see if this might play a role / affect the timbre of the comb-filtering. It does not; Bypass and Stereo had the same sound (i.e. same timbre) and the Upsample mode had a lower pitch to it just as before.]

[ADDED 04/12/12: I have just uploaded the simulations that I did to find out if what I was hearing from the 990 was akin to comb-filtering; I have spoken of this in the thread (and the other thread), but I decided to post the simulations so that they could be compared against the actual data. Again, these files are synthesized. That is, these are NOT from the 990, but instead are files that I created to see if a simple delay-and-add was representative to the issue that I am hearing in my 990. TO generate these files, I performed a delay-and-add process using 1 ms, 3 ms, 5 ms, 8 ms (which corresponds to the delay observed in the STEREO and BYPASS modes), 9.3 ms (which corresponds to the delay observed in the UPSAMPLE mode), and lastly, 50 ms. The files appear in a folder called "synthesized_comb_filtering_examples". Each file is 30 seconds in length, two-channel, and is availavle in .wav, .flac, and .mp3 formats (a sub-folder exists for each format).

Note that if you compare the 8 ms and the 9.3 ms delay-and-add synthesized files to the actual data from the 990, you will hear that they bear a striking resemblance; compare the 8 ms synthesized file to the FRONT STEREO or the FRONT BYPASS files posted earlier and you will hear...likewise for comparing the 9.3 ms synthesized file to the FRONT UPSAMPLE file.

One note of caution - I did not normalize the magintude of the files, so some may play louder than others, but you can easily adjust the gain in your media player / app / device that you use to audition these; the thing of import is the timbre (character) of these synthesized versions as compared to the actual data obtained from the 990.