Become a Site Supporter and Never see Ads again!

Author Topic: Probably a dumb question (DC offset)  (Read 414 times)

0 Members and 1 Guest are viewing this topic.

Offline heathen

  • Trade Count: (3)
  • Taperssection Regular
  • **
  • Posts: 119
Probably a dumb question (DC offset)
« on: July 14, 2017, 11:40:04 PM »
In the attached image, is the part circled in red DC offset?
Recording: Countryman B3 | CA-14 omnis | CA Ugly BB | AKG 460/ck61 | Studio Projects CS5 | Tascam DR-70D | Roland R-05
Playback: Monitor Audio Silver 10 | NAD C 275BEE | Emotiva TA-100
Headphones: Beyerdynamic DT 880 | ATH-M50 | Violectric HPA V90 | Raspberry Pi | HiFiBerry DAC+ Pro

Offline bombdiggity

  • Trade Count: (11)
  • Needs to get out more...
  • *****
  • Posts: 2021
Re: Probably a dumb question (DC offset)
« Reply #1 on: July 17, 2017, 02:33:48 AM »
DC offset deals with the entire segment not a tiny segment of it. 

"DC offset is a mean amplitude displacement from zero. In Audacity it can be seen as an offset of the recorded waveform away from the center zero point. DC offset is a potential source of clicks, distortion and loss of audio volume."
 
DC offset - Audacity Development Manual
manual.audacityteam.org/man/dc_offset.html

There's a dramatic illustration of what it could look like there ^. 
Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline Gutbucket

  • record > listen > revise technique
  • Trade Count: (13)
  • Needs to get out more...
  • *****
  • Posts: 11239
  • Gender: Male
Re: Probably a dumb question (DC offset)
« Reply #2 on: July 17, 2017, 10:22:43 AM »
That image shows a plot of voltage over time, with the change in voltage representing pressure variations. See how the area you've circled undulates above and below the zero voltage line?  The center of undulation indicates the average voltage value.  If that center value was constantly above or below the zero voltage line over the entire length of the file, it would indicate the presence of DC offset.  A recording system intentionally sensitive to zero-hertz pressure variations acts as a barometer.  Since audio recording systems are designed to measure pressure variations only in the audible range, with a sensitivity that intentionally drops off to nothing before reaching zero hertz, significant DC offset in an audio recording system indicates something may be incorrect in the signal chain.  Or that Jimmy Cliff is in town.

« Last Edit: July 17, 2017, 02:01:15 PM by Gutbucket »
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

Offline bombdiggity

  • Trade Count: (11)
  • Needs to get out more...
  • *****
  • Posts: 2021
Re: Probably a dumb question (DC offset)
« Reply #3 on: July 17, 2017, 12:27:53 PM »
Great breakdown (as usual) ^. 

I've noticed that certain pre's have a defined DC offset.  For example my Tinybox runs at .03% every time and always has.  My Oade modded R-44 always exactly at 0%, running the same mics (the only other difference in the chain being the cables).  I can't say I hear anything amiss with the sound of the Tinybox though I always correct it in editing. 

Old analog sources (like cassettes) transferred to digital tend to show much larger DC offsets.  Sometimes different offsets in each channel.  Cassette recordings almost always have an offset. 

Some instruments will appear to have much greater energy above the zero voltage line than below (mostly brass ones) and it can look to the eye like the recording would have to have a large offset but when you check the stats it doesn't. 

It is easy to get a read on it just by pulling the stats on a file in your editor and easy to correct.  See the other recent thread about correcting in Audition. 

Gear:
Audio:
Schoeps MK4V
Nak CM-100/CM-300 w/ CP-1's or CP-4's
SP-CMC-25
>
Oade C mod R-44  OR
Tinybox > Sony PCM-M10 (formerly Roland R-05) 
Video: Varied, with various outboard mics depending on the situation

Offline heathen

  • Trade Count: (3)
  • Taperssection Regular
  • **
  • Posts: 119
Re: Probably a dumb question (DC offset)
« Reply #4 on: July 17, 2017, 12:43:51 PM »
Thanks for the info guys.  Bottom line: is the above anything to worry about?
Recording: Countryman B3 | CA-14 omnis | CA Ugly BB | AKG 460/ck61 | Studio Projects CS5 | Tascam DR-70D | Roland R-05
Playback: Monitor Audio Silver 10 | NAD C 275BEE | Emotiva TA-100
Headphones: Beyerdynamic DT 880 | ATH-M50 | Violectric HPA V90 | Raspberry Pi | HiFiBerry DAC+ Pro

Offline Moke

  • Trade Count: (2)
  • Needs to get out more...
  • *****
  • Posts: 2998
  • m0k3 - √!n¥¬ 633|<
Re: Probably a dumb question (DC offset)
« Reply #5 on: July 17, 2017, 02:05:29 PM »
That image shows a plot of voltage over time, with the change in voltage representing pressure variations. See how the area you've circled undulates above and below the zero voltage line?  The center of undulation indicates the average voltage value.  If that center value was constantly above or below the zero voltage line over the entire length of the file, it would indicate the presence of DC offset.  A recording system intentionally sensitive to zero-hertz pressure variations acts as a barometer.  Since audio recording systems are designed to measure pressure variations only in the audible range, with a sensitivity that intentionally drops off to nothing before reaching zero hertz, significant DC offset in an audio recording system indicates something may be incorrect in the signal chain.  Or that Jimmy Cliff is in town.



In a van down by the river of babylon.

carry on.
Sent From My Craftsman Garage Door Opener

Offline perks

  • Trade Count: (21)
  • Needs to get out more...
  • *****
  • Posts: 4066
Re: Probably a dumb question (DC offset)
« Reply #6 on: July 17, 2017, 02:21:40 PM »
I'm a bit dense but is this due to the pressure (SPL) is going to drop on you?
Mics: Schoeps MK5, Schoeps MK41, AT853u (C,SC,H)
Preamps/converter: Schoeps VMS52UB (x2), Nbox (x2), Grace Lunatec V2, Sound Devices MP-2, DPA MMA6000, Naiant Tinybox v1.5, Benchmark AD2k+
Recorders: Tascam DR-680, Korg MR-1, Edirol R-05, Sony M10

Offline Gutbucket

  • record > listen > revise technique
  • Trade Count: (13)
  • Needs to get out more...
  • *****
  • Posts: 11239
  • Gender: Male
Re: Probably a dumb question (DC offset)
« Reply #7 on: July 17, 2017, 02:40:01 PM »
Cuban missile crisis as alternate metaphor- When your ports get blocked the pressure gonna rise!

heathen, no offset worries in the file you posted the image from.  And minor amounts of offset like those mentioned above with regards to various preamps and recorders and sources which produce somewhat asymmetrical waveforms such as horns are likewise not a problem.  Like Bombiggity suggests, if you suspect an issue, the easiest way to check is to take a look at the file/waveform stats.
volition > vibrations > voltages > numeric values | numeric values > voltages > vibrations > virtual teleportation time-machine experience

 

RSS | Mobile
Page created in 0.147 seconds with 31 queries.
© 2002-2017 Taperssection.com
Powered by SMF
Website Design by Foxtrot Media, Inc., a Baltimore Website Company