IPB

Welcome Guest ( Log In | Register )

RMAA fails to pick-up audible hiss, reports nearly perfect noise level
skamp
post May 1 2013, 10:51
Post #1





Group: Developer
Posts: 1413
Joined: 4-May 04
From: France
Member No.: 13875



We've been scratching our heads about this on Anything but iPod and in #rockbox on Freenode. With sensitive IEMs (like my Shure SE425s), there's a faint, but audible, hiss with the Rockboxed Fuze+, when no music is playing. The hiss is a lot more pronounced when playing a digitally silent file. I don't hear hiss with the iPod Classic. At least 2 other people have made the same observation.

The problem is, RMAA can't seem to pick it up. The Fuze+ gets exactly the same noise and dynamic range scores as the Classic, unloaded as well as loaded with the Shures and the Denons: 95dB, a nearly perfect score for a 16 bit device. More to the point, while the Fuze+ and the Classic are audibly different (with regards to hiss), why do they get identical scores in all situations?

You could slap me with the TOS #8 hammer, but I don't know how we can prove what we hear. The difference is easily heard when turning the Fuze+ on and off. And since we can't determine the nature of the noise, or its cause, the Rockbox developer (pamaury) doesn't really know what to do about it, or if it's even fixable at all.

I'm no electrical engineer. Is there something special about what we perceive as "hiss", that would be audible, but that wouldn't show up in RMAA-type tests / recordings? There's no way I could hear noise if it actually was at -95dB.

I have no idea if this is relevant, but FWIW, the Fuze+ has an output impedance of 0.9Ω, and the iPod Classic, 5.5Ω. The Shures are 22Ω / 109 dB/mW, and the Denons are 25Ω / 100-106 dB/mW (depending on whom you ask).

Edit: I forgot that I already mentionned that problem, but it's bugging me, and I guess it doesn't hurt to start a dedicated thread.

This post has been edited by skamp: May 1 2013, 10:55


--------------------
See my profile for measurements, tools and recommendations.
Go to the top of the page
+Quote Post
 
Start new topic
Replies
skamp
post May 1 2013, 11:42
Post #2





Group: Developer
Posts: 1413
Joined: 4-May 04
From: France
Member No.: 13875



I don't think that's working properly. RMAA reports a noise level of -18.6dB with both my Fuze+ and my O2/ODAC (which is not possible, it's dead silent).


--------------------
See my profile for measurements, tools and recommendations.
Go to the top of the page
+Quote Post

Posts in this topic
- skamp   RMAA fails to pick-up audible hiss   May 1 2013, 10:51
- - bennetng   RMAA always add dither in its test signal so you a...   May 1 2013, 11:03
- - skamp   You must have done something wrong, your sample la...   May 1 2013, 11:23
|- - bennetng   QUOTE (skamp @ May 1 2013, 18:23) You mus...   May 1 2013, 11:28
- - Brazil2   Maybe give Visual Analyser a try: http://www.silla...   May 1 2013, 11:23
- - skamp   I don't think that's working properly. RMA...   May 1 2013, 11:42
|- - bennetng   Try to uncheck the following in RMAA before testin...   May 1 2013, 11:47
- - skamp   I did that. RMAA wouldn't accept the file if I...   May 1 2013, 11:50
|- - bennetng   Full test file http://s000.tinyupload.com/index.ph...   May 1 2013, 11:57
- - skamp   Thanks. Dynamic Range is still the same (95dB), wh...   May 1 2013, 14:22
|- - bennetng   Do you mean you can still hear the hiss but the me...   May 1 2013, 14:46
|- - skamp   QUOTE (bennetng @ May 1 2013, 15:46) Do y...   May 1 2013, 15:01
- - skamp   Also note that RMAA does pick up noise, when it...   May 1 2013, 15:05
- - 2Bdecided   Could the maximum signal output vs the background ...   May 1 2013, 15:13
|- - skamp   QUOTE (2Bdecided @ May 1 2013, 16:13) Cou...   May 1 2013, 15:18
|- - 2Bdecided   QUOTE (skamp @ May 1 2013, 15:18) Surely ...   May 1 2013, 15:27
|- - bennetng   In RMAA's test signal, 2.5s to 6.5s is the noi...   May 1 2013, 15:44
- - saratoga   My guess is that you don't have enough dynamic...   May 1 2013, 17:59
|- - skamp   QUOTE (saratoga @ May 1 2013, 18:59) My g...   May 1 2013, 18:05
|- - saratoga   QUOTE (skamp @ May 1 2013, 13:05) QUOTE (...   May 1 2013, 18:29
|- - skamp   QUOTE (saratoga @ May 1 2013, 19:29) Is t...   May 1 2013, 18:45
|- - Arnold B. Krueger   QUOTE (saratoga @ May 1 2013, 13:29) QUOT...   May 3 2013, 13:47
- - 2Bdecided   So if you just record using your equipment the noi...   May 3 2013, 10:05
- - skamp   I find this all very confusing, so instead of draw...   May 3 2013, 11:06
|- - bennetng   QUOTE (skamp @ May 3 2013, 18:06) Note th...   May 3 2013, 11:49
- - 2Bdecided   Your files show identical behaviour in both condit...   May 3 2013, 15:08
- - stephan_g   The amount of dynamic range required in measuremen...   May 5 2013, 23:56
- - stv014   Tests in this other thread suggest that the noise ...   May 6 2013, 10:04


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 2nd August 2014 - 00:03