Identify Dolby NR

[magikarp99]

Is there a solid method of determining whether a tape has been recorded using Dolby B noise reduction?

Could it be determined by looking at a spectrogram or spectrum histogram?

[hech54]

This is a joke right?

[magikarp99]

This is a joke right?

I do love it when you reply to posts with snide comments and no real content.

[davexnet]

Are you talking about audio cassette ? I could always tell be listening to it.
If playing back with Dolby turned on removed all the high frequencies so that it sounded dull, most likely it
was recorded without Dolby.
Likewise if playback with Dolby turned off plays back with emphasized high frequencies, Dolby was probably
used in the recording.

[El Heggunte]

And I think this topic is rather misplaced (a.f.a.i.k., Dolby NR is not video capture ).

[magikarp99]

You are right that this is probably better in the audio capture forum, my mistake.

I'm talking about Dolby B NR on VHS tapes, but it should be the same as on other formats too I guess.

The recording doesn't have many high frequencies, the frequency response goes up to about 10KHz. I was just wondering if there was a more quantitative way of determining this than just listening and deciding which sounds better. It seems that there really must be.

[davexnet]

I didn't even know there was a VHS deck that used Dolby stereo on the linear tracks.

[magikarp99]

I didn't even know there was a VHS deck that used Dolby stereo on the linear tracks.

Some did https://en.wikipedia.org/wiki/Vhs#Original_linear_audio_system

[johns0]

My parents have a 1980 front loading jvc with linear stereo with dolby b,cost them $1100 at the time.It's currently stored away.

[Cornucopia]

You MIGHT be able to determine the difference statistically based on expected vs. actual power distribution of the frequency spectrum, but that would never be even close to reliable unless the material in question was prefaced with accompanying Dolby calibration tones.
And, as an old school analog process, it doesn't have any flags or metadata.

So your best bet is to do what was already suggested and guess.

Scott

[Hoser Rob]

Yes, it is frakking obvious. Listen to it.

[turk690]

I'm talking about Dolby B NR on VHS tapes, but it should be the same as on other formats too I guess.

Dolby B NR on VHS linear track audio? Gosh a domestic machine for that is probably around 1980. Amazing if it's still working

[magikarp99]

Many many professional decks have Dolby B NR built in. This includes professional decks produced right up to the end of VHS's lifetime.

[Cornucopia]

Yes, it is frakking obvious. Listen to it.

Except in real life, historically, it never has been OBVIOUS. That's part of the reason one needed to use calibration tones on professional masters. That's also the reason Dolby B was chosen to be used on the great majority of audiocassettes - it is relatively weak & doesn't change things that much (so it can't "ruin" it too much if it is misjudged, which it often could be).

If you aren't very familiar with the recorded material to begin with, and don't know the relative quality of your sound medium (tape material consistency), you have little way of knowing if the sound you were hearing was SUPPOSED to be mixed that way, or rather that there may have been some mis-adjustment with the playback head azimuth/interchange, and/or deterioration in the recorded sound.

Scott

[johns0]

Dolby b sounds the best on the original deck it was recorded on,on other decks with heads that are misaligned then it would sound like crap.

[NJRoadfan]

Dolby b sounds the best on the original deck it was recorded on,on other decks with heads that are misaligned then it would sound like crap.

VHS linear tracks don't quite have the issues with azimuth and alignment that compact cassette has.

That being said, tapes with Dolby NR on VHS linear tracks are rare. Unless you have a tape with dual linear tracks, you won't encounter it. The only consumer decks with linear stereo were produced in 1983-86 and were high end and uncommon. Professional editors had it too, but you won't run across too much of those outside of high school and university TV studios.

[johns0]

Have you ever worked on vcrs?They do have alignment problems especially in the ep mode and the linear audio tends to skew in sound.

[pandy]

Is there a solid method of determining whether a tape has been recorded using Dolby B noise reduction?

Could it be determined by looking at a spectrogram or spectrum histogram?

Generally yes but it can be not conclusive (as level is variable):
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape5.html
http://www.pacificav.com/library/dolbybcsnoisereduction.html
http://www.hansvanzutphen.com/tape_restore_live/help/1.0/dolby_b_filter.html

[magikarp99]

Yes, it is frakking obvious. Listen to it.

Except in real life, historically, it never has been OBVIOUS. That's part of the reason one needed to use calibration tones on professional masters. That's also the reason Dolby B was chosen to be used on the great majority of audiocassettes - it is relatively weak & doesn't change things that much (so it can't "ruin" it too much if it is misjudged, which it often could be).

If you aren't very familiar with the recorded material to begin with, and don't know the relative quality of your sound medium (tape material consistency), you have little way of knowing if the sound you were hearing was SUPPOSED to be mixed that way, or rather that there may have been some mis-adjustment with the playback head azimuth/interchange, and/or deterioration in the recorded sound.

Scott

This is what I have found too.

Is there a solid method of determining whether a tape has been recorded using Dolby B noise reduction?

Could it be determined by looking at a spectrogram or spectrum histogram?

Generally yes but it can be not conclusive (as level is variable):
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape5.html
http://www.pacificav.com/library/dolbybcsnoisereduction.html
http://www.hansvanzutphen.com/tape_restore_live/help/1.0/dolby_b_filter.html

Thanks for the links.