The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
The mysterious case of the dissappearing headroom (please help - files attached) Keyboard Synthesizers
Old 7th September 2011
  #1
Gear Addict
 

The mysterious case of the dissappearing headroom (please help - files attached)

I have just encountered something very strange whilst testing out the line input of a neve 34127 preamp.

I was trying to test out what sort of difference there was soundwise between it and the line in on my chandler ltd1. I programmed an impromptu synth line on my midi'd juno 60 and ran the left out of the juno 60 into the 34127 and the right out into the ltd1. I then level matched them within .01db using the meters in ableton (with the intention of flipping the phase on one channel so I could hear the difference). Here is where it gets weird. It was quite obvious that although they were level matched using the meters that the ltd1 was considerably louder (like 5db or so). My radioshack meter confirmed this. The same thing happens when I run the same test but instead of using the ltd1 I use the line in on my lynx two card.

If I put a Spectrum analyzer on the channels and then level match the fundamental note - the files sound extremely similar level-wise but SOMEWHERE in the recordings of synths run through the 34127 4-5db of headroom dissapears (ie. the files need to read 5 or so db louder on the meters to match identical files volumewise).

I cannot find anything that explains this... the spectrums of the files looks extremely similar yet one is perceived as 5db softer for the same volume on ableton's meters...

Attached are three files which might better help to explain this.
Sh1011.wav is 1note repeated on my sh101 and run through the 34127
sh1012.wav is the exact same note run straight into my lynxtwob and then level matched to sh1011.wav on the meters in ableton to .01db
sh1013.wav is sh1012.wav level matched to the fundamental of sh1011.wav in ableton's spectrum analyzer (the harmonics appear matched aswell)

Could somebody please analyze these files and try and explain to me why sh1012.wav is perceived as 5db louder than the other two files - yet measures identically on all the meters I could test it on? (I couldn't find any narrow band resonances or dc or anything)

If this is better placed somewhere else in the forum I apolagise...

If my post is confusing... I'm sorry - it's pretty difficult to explain this...

Thanks,
Mike
Old 7th September 2011
  #2
Gear Addict
 

sorry... files should be attached in this post now!
Attached Files

sh1011.wav (435.2 KB, 122 views)

sh1012.wav (435.2 KB, 151 views)

sh1013.wav (435.2 KB, 193 views)

Old 7th September 2011
  #3
Registered User
Can't listen here at work, but have you done a null test? You should then be able to hear the difference.

I'm guessing one path rounds of some transients, so when you match peak levels you are boosting average level.
Old 7th September 2011
  #4
Gear Addict
 

Quote:
Can't listen here at work, but have you done a null test? You should then be able to hear the difference.

I'm guessing one path rounds of some transients, so when you match peak levels you are boosting average level.
A good point - unfortunately for that to be the case the 34127 would have to be adding transients as it is the one that is softer sounding. If you listen to the files they are of a single note on an sh101 and aren't exactly dynamic and transient rich...
Old 8th September 2011
  #5
Lives for gear
 

Quote:
Originally Posted by africantigercow View Post
Could somebody please analyze these files and try and explain to me why sh1012.wav is perceived as 5db louder than the other two files - yet measures identically on all the meters I could test it on?
Did you try an rms meter? Sample peak meters can't show you anything specific at all about perceived loudness.

SH1011: peak = -11.64, rms = -19.39
SH1013: peak = -15.63, rms = -19.31
SH1012: peak = -11.64, rms = -15.32 <<<<

see?
Old 8th September 2011
  #6
Registered User
Since I can't listen I should probably shut up, but that's never stopped me before ...

Are these two seperate takes? And were you using the chorus in the SH101? The reason I ask is that there won't be any repeatability between two takes from the same synth, even triggered with the exact same midi notes. The chorus LFO (and probably the PWM LFO if that was used) would be free running, and a chorus is basically a sweeping notch filter that causes peak resonances. So the effect, on top of your ADSR from the DCO would be random from take to take.

I found this to be the case even with virtual synths ... to compare preamps, I would advice recording the synth so you can use the exact same source signal each time.
Old 9th September 2011
  #7
Gear Addict
 

Quote:
Did you try an rms meter? Sample peak meters can't show you anything specific at all about perceived loudness.

SH1011: peak = -11.64, rms = -19.39
SH1013: peak = -15.63, rms = -19.31
SH1012: peak = -11.64, rms = -15.32 <<<<

see?
I get that... but it's not exactly a dynamic source? it's a constant level source... on both files when I look at the meter - the meter literally doesn't move. Also how is it that (when they are both running through my lynx card) the neve lowered the rms? wouldn't that mean it has to have added transients or increased the dynamic range (or something?)
Old 28th September 2012
  #8
Gear Addict
 

Just out of interest - I think i figured out what was happening here -

DC offset in one direction would raise the peak level without raising the rms?

Is that true?
Old 28th September 2012
  #9
Lives for gear
 
stinkyfingers's Avatar
 

looking at the statistics, i don't see any significant DC offset in those files...
once they are RMS level matched, notice that 1012 and 1013 are the same...you can barely see red traces under the blue...(pic)
i think the 1011 file has a higher peak level ("spikes") because of phase shift or something...
Attached Thumbnails
The mysterious case of the dissappearing headroom (please help - files attached)-sh.jpg  
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump