Talk:Transparency (data compression)

message: Needs a example after the first paragraph. Something like this... (please improve on the phrasing or give a better example)
"For example, when encoding an image, a group of pixels with a small colour difference may be assigned just one colour between them. This would improve the compressibility of the data. The smaller the colour difference, the more transparent the compression."  —Preceding unsigned comment added by 82.7.196.141 (talk) 08:53, 10 July 2010 (UTC)
thread_title: Method or Example

message: I agree about testing being difficult. Personally I am aware that my hearing is not always in the same condition - sometimes I have wax in my ears, and sometimes even signs of tinnitus.
Superficially for MP3 at 192 kbps I can't tell the difference between most CDs and the encoded version. However if I listen to the music while encoding, I can tell that there are some critical parts where there is a perceptual loss even with 192 kbps encoding. These are infrequent perhaps only a few seconds in a long piece of music, but often these are the parts where I feel "wow" in a good recording. The MP3 encoding will often remove the wow factor.
In order to do a fair test the recordings used should be good. In my opinion, many people, even some with quite impaired hearing, can tell the difference between a good recording and a poor one. Recently in a blind test I was asked about the quality of 160, 128 and 64 kbps (I think) MP3 files. I was not given access to the original recording. There was little difference between the 160 and 128 kbps encoded material. There was a harshness in the string sound (orchestral, Tchaikovsky - Serenade for Strings) which very probably did not reflect the sound of the orchestra. The low bit rate recording did not have too many obvious MP3 artefacts, and it was clear that it had a smoother, but also possibly duller frequency response. I chose that as my preferred version - to the amusement of the testers. However if I'd been given a reference recording, or been asked to do an ABX comparison I would probably had been able to do that. The point I'm making here is that the filtering of high frequency sounds in the particular source actually made it pleasanter to listen to. Also I thought that the stereo separation was better in the low bit rate version. I would have expected a really high quality sound source to have sounded smooth, but also significantly less dull than the low bit rate recording.
Where this kind of testing is carried out, the testers really do need to know what they are doing. Significant care needs to be taken when generating the encoded material, and possibly some familiarity with the music used for testing, and the nature of artefacts in the encoding process will help the testers to develop material for a valid test.
In the limit, for higher quality encoding, the differences may be very subtle and small, and doing the evaluation of subjects could be very hard. It is possible that some differences in the sounds perceived may be slight modifications and have little to do with the encoding. These could include level differences and frequency response differences. For me after reading about the MAD MP3 decoder I've been using Winamp 2.95 with the MAD decoder in preference to newer versions of Winamp (see http://en.wikipedia.org/wiki/Talk:Transparency_%28data_compression%29 ). There are articles which tell me that this should sound better than the standard decoder. I am thus pre inclined to prefer this, even if I really cannot tell the difference. I feel however that I can actually detect a difference and recordings do sound pleasanter, more real, and more involving, but this could be due to frequency changes rather than the finer resolution of the decoding due to the dithering used. I have no way of knowing this, and only an independent test would establish this in my perception. I suppose I could evaluate the frequency content of samples using different versions of Winamp to determine whether frequency modifications are a possible explanation of my preference for the MAD decoded data.
David Martland 11:01, 3 May 2007 (UTC)
thread_title: Testing

message: Age of listener, and other factors (noisy work environment, frequent firearms usage or loud music environments w/o ear protection, etc.) are a major factor, too, but not mentioned. With treble especially, younger, less pounded ears are far, far more sensitive (enough so that there are are joke Android/iOS apps called "teen annoyers" that make startling high-pitched sounds people older than about late 20s can't hear at all.  This does have an effect on music perception.  In particular, younger people tend to jack the bass up to levels that seem drowning to older ears, because for them everything is swimming in treble they won't be able to hear in a decade or two.  Please don't throw a "cite some sources or shut up" asinine remark at me; I'm not proposing a major revision to the article (about which I care little; my watchlist is HUGE). Just suggesting that something is missing, and those who do watch this one could improve it in that direction if they get some time to go digging around for sources. 68.84.153.245 (talk) 18:44, 11 December 2011 (UTC)
thread_title:  Acuity