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Topic: Can signal analysis confirm presence of Dolby NR or pre-emphasis? (Read 8212 times) previous topic - next topic
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Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Sometimes, when there's a particularly treble-y, "bright" mastering on CD, people wonder if the disc was mastered with pre-emphasis, but without having had any flags properly set in the TOC or subcode. Similarly, some tracks on some CDs are suspected to have been sourced from Dolby-encoded master tapes which were played without Dolby noise reduction at some point in the mastering chain.

It's assumed that there's no way to know for sure that there's pre-emphasis or Dolby NR, but is that really true? I figure it must be, but you guys are the technical experts; you tell me...

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #1 –
IMO without a reference you can't be objectively sure but you can make a good subjective guess.

Pre-emphasis is just an EQ - applying pre-emphasis (and not flagging it) will sound the same as adding a similar EQ (to a recording that really didn't need it).

Depends what Dolby you mean. I don't think they ever use consumer Dolby in studios, though I'm not sure about video soundtracks on the semi-pro analogue formats. I don't know what undecoded professional Dolby A sounds like. I know what undecoded dbx sounds like, and no one would put that out by mistake.

Dolby has a frequency signature to it, but it's level dependent and has time-domain issues too. If you know what to listen for, it's easily identifiable. The only way to mistake it is if someone has made some very strange amplitude dependent EQ choices (i.e. EQ + compression) and/or added a bit "too much" reverb.


If I don't like the EQ on something, I tend to change the EQ without worrying too much about why it might be "wrong".


With a reference (e.g. multiple releases of the same material) then you can make comparisons, plot the EQ differences, and maybe make an objective call when the difference very clearly matches the pre-emphasis curve. Any intentional mastering EQ on top makes this subjective again though.

Cheers,
David.

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #2 –
Inevitably, someone will sooner or later ship the wrong master tape. Skinny Puppy's "Rabies" was released on CD with Dolby B: http://en.wikipedia.org/wiki/Rabies_%28Ski...e_and_promotion

(For this album they even shipped out the wrong recording: http://www.metal-archives.com/albums/Sodom...by_Cruelty/3095 , see the "Additional notes" tab.)

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #3 –
Quote from: mjb2006 on
Sometimes, when there's a particularly treble-y, "bright" mastering on CD, people wonder if the disc was mastered with pre-emphasis, but without having had any flags properly set in the TOC or subcode. Similarly, some tracks on some CDs are suspected to have been sourced from Dolby-encoded master tapes which were played without Dolby noise reduction at some point in the mastering chain.

It's assumed that there's no way to know for sure that there's pre-emphasis or Dolby NR, but is that really true? I figure it must be, but you guys are the technical experts; you tell me...


It is really true that conclusively determining the provenance of any recording is impossible. 

Audio forensics can provide relevant evidence and in some cases the evidence can be so clear that it can lead to a conclusion. In general that is not always the case or the case often enough to be really useful.

Probably the best evidence may be what you already know - there is this recording that is particularly treble-y or bright.  Did it get that way because of the kinds of technical errors you mention? Did it get that way because the mastering engineer had a head cold that day?  Did it get that way because the producer had something in mind?  Who knows?

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #4 –
Hopefully the master would have test tones and with someone paying attention they would notice something was wrong.

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #5 –
Quote from: Arnold B. Krueger on
Quote from: mjb2006 on
Sometimes, when there's a particularly treble-y, "bright" mastering on CD, people wonder if the disc was mastered with pre-emphasis, but without having had any flags properly set in the TOC or subcode. Similarly, some tracks on some CDs are suspected to have been sourced from Dolby-encoded master tapes which were played without Dolby noise reduction at some point in the mastering chain.

It's assumed that there's no way to know for sure that there's pre-emphasis or Dolby NR, but is that really true? I figure it must be, but you guys are the technical experts; you tell me...


It is really true that conclusively determining the provenance of any recording is impossible. 

Audio forensics can provide relevant evidence and in some cases the evidence can be so clear that it can lead to a conclusion. In general that is not always the case or the case often enough to be really useful.

Probably the best evidence may be what you already know - there is this recording that is particularly treble-y or bright.  Did it get that way because of the kinds of technical errors you mention? Did it get that way because the mastering engineer had a head cold that day?  Did it get that way because the producer had something in mind?  Who knows?



On balance, the audible coloration of a recording that needs Dolby processing in order to sound right is characteristic enough that one can learn how to identify it in many cases.

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #6 –
That goes back to my question, though... having a feel for the sonic "color" of Dolby NR is nice for you, but I am wondering if there is anything that the rest of us can actually measure or at least keep an eye out for (like how you can spot the "shotgun blast" effects of some lossy codecs in spectrograms).

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #7 –
Quote from: mjb2006 on
That goes back to my question, though... having a feel for the sonic "color" of Dolby NR is nice for you, but I am wondering if there is anything that the rest of us can actually measure or at least keep an eye out for (like how you can spot the "shotgun blast" effects of some lossy codecs in spectrograms).


I recommend that you train your ears by Dolby encoding some files or finding such files already encoded, and listening to them without Dolby decoding.
 

Can signal analysis confirm presence of Dolby NR or pre-emphasis?

Reply #8 –
You can recognize FM Radio pre-emphasis quickly if you ever worked with that stuff (one of the most unpleasant boost of high frequencies for sure).  It's easy to know the presence of Dolby NR on a compact audio cassette tape, it's usually on the package or tape itself and can be corrected with software (Tape Restore Live) (although it have to calibrated to make sure the removal isn't too much or too little).

As for CDs, it's hard to know short of someone listing something on the package, the disc, booklets or a flag being set correctly.  To be honest I never encountered a CD with pre-emphasis at all.  I know some albums or songs can be a little bright but not to the point of me thinking it was pre-emphasis.  I don't have much experience here.  Pre-emphasis is pointless on CDs.  I know some devices like headphones or speakers might color the sound of something with a lot of high frequency energy and make it sound like the treble was bumped a bit similar to the effect of pre-emphasis.  Unless something is unpleasantly bright to begin with, where you find yourself lowering the treble a lot there is no real way of knowing for certain.  Although it's possible to recognize it and correct it, if you find it in the recording.  Something that's unusually bright for the genre of that time period might be a hint, although someone could of decided that bright EQ work was better too.