Go Back   Home > Forums > General Interest > diyAudio.com Articles

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Comment
 
Article Tools Search this Article
Old 29th March 2011, 10:57 AM  
Pano is offline Pano  United States
diyAudio Moderator
 
Pano's Avatar
 
Join Date: Oct 2004
Location: Milliways
Blog Entries: 4
Default What is Gain Structure?

Gain structure (AKA Gain Staging) is a concept that gets talked about a lot in pro audio, but most home audio folks have never heard of it. Understanding gain structure can help you get the cleanest signal possible out of your system and avoid some nasty things. Things like noise and clipping,...

Last edited by Variac; 1st April 2011 at 11:34 PM.
  Reply With Quote
7th February 2013
gpapag's Avatar
gpapag
diyAudio Member
Pano
Great write. Thank you.
Although we are concerned here with playback on commercial recordings where mastering has already taken care of high peaks, VU meter readings is much lower from Peak meter dbs. With classic and opera works, Peak meter readings are between 12db and 18db higher than VU meter dbs .
diyAudio
I’ve seen up to 24db difference.

Therefore, the 6db overhead that is mentioned, it should be applied to Peak meter indicators. If the instrument is a VU meter, the overhead has to be a conservative 20db.

That the meters are implemented in the software, it doesn’t mean that they are designed to respond to the signal's impulsive content instantaneously.
Even when one is monitoring through the digital bit depth meter (dbs rel dbFS ) , he has to know the “ballistics” of that particular instrument. Not every SW supporting documentation makes things clear on this.

George
["Second Law is a bitch." - SY] ["The Road To Heaven:Specify the performance & accept the design. The Road To Hell:Specify the design & accept the performance"-Bruno Putzeys]
23rd July 2014
Jamesblond
diyAudio Member
Great article. Explanation is spot on. I've worked as a professional recording and mix-engineer, both live and in the studio. Maintaining a good, healthy and clean signal throughout a complex system, can be a challenge. Especially when you add devices that add frequency-specific amplification (or attenuation), like EQ's. Compressors in the chain can increase noise problems dramatically!

The only point of criticism I have about this article, is the mention of the DCX2496 digital active cross-over processor. It's said to be meant for "the pro-audio world". Let me rectify that.

The DCX2496 is a Behringer device. This device may offer a buch of features that are quite interesting for hifi-enthousiasts who want to expand their systems (multi-amp processing, for example), in terms of sound quality is certainly isn't the best choice. Behringer, although it has a good reputation of delivering "bang for buck", is a brand not frequently used or loved in the higher ranges of the pro-audio world. It simply doesn't deliver the sound quality required in most hi-end studio's or hi-end PA systems. This has to do with durability, S/N ratio, linearity and accuracy of the AD/DA conversion, linearity of the input and output stages, etc. Since most well-developed home-audio systems sound as good as some studio systems, it would be a shame to expose them to a component that sounds not as good as it should.

If you want a device with similar functionality, look at names like DBX, BSS minidrive or omnidrive, Dolby or Electro Voice. Really. These can be had on the used market for decent prices. Still more expensive than a new Behringer, but your ears will love you for it. Quality comes at a price - that's a universal truth.

Let me add that since Behringer acquired the Midas brand, they have incorporated a bunch of Midas technology into their own designs. That can only be a good thing. Take a look at the X32 mixing desk, for example. Tons of features and good sound at a competitive price. At the moment, however, there is no Behringer active cross-over on the market with Midas technology in it.
23rd July 2014
Jamesblond
diyAudio Member
Antoinel: "I advocate the design doctrine of Nelson Pass which is: "keep it simple". A CD player has a volume-controlled headphone amp. It is a high fidelity mini power amp ~15-20mW (rms) into 30 Ohm loads. The CD player's volume control may be manual (e.g. Marantz), or motorized via a remote controller (Sony). The resultant output then goes directly to the input of the power amp. This approach is a high efficiency and least-noise gain structure."

Adason: "while it is feasible, to put headphone cd output straight to the amp, it usually does not sound very good. The reason is that the best cd players do not have headphone output at all, those who have have it for some sort of monitoring, not for real listening. Well, I tried it, it just does not compare with dedicated high quality headphone amp fed by line signal. The line level out can be high quality, but headphone amp inside cd player is usually of mediocre quality. Most of the time one OPA. Rarely discrete. Never tube headphone output. If yes, please point me to such cd player."

I agree that connecting a headphone output direcly to the line-input of a (pre-)amp is not a very good idea. You might get away with it on some pro-audio gear (with low input impedance - 600Ohms or so), but not with most cosumer gear. The reason for this is output-to-input impedance matching. A 30 Ohm output will not drive a 47+ kOhm input very efficiently, resulting in suboptimal sound. Usually thin sounding low end and, brittle highs and no real 3D-scale in the sonic image. Not to mention added distortion because of the simple headphone amp, that was not designed for critical listening sessions.
23rd July 2014
Pano's Avatar
Pano
diyAudio Moderator
James - thanks! Glad you like it. I hope that it will give users unfamiliar with the concept something to thing about and a basis for improving signal flow.

Quite right that it gets even more complicated when filters and compressors are added. That can take some real juggling. Most home users have no idea how complex live sound can get.

I agree and disagree on the DCX2496. Yes, in stock form it ain't pretty sounding, but if you search the forums here you will find that there is a quite a bit of modifying going on. Mostly it's the analog sections of the DCX that suck, followed by the power supply and maybe the clock. But the A/D, DSP and D/A are quite good, really I have a DBX Driverack 480 here and it uses many of the same AKM chips. It just has more in/outs and a much better analog section than the Behringer.

Have you used any of the Bi-Amp processors? We use them now at work and they are very nice. We replaced the DBX with a Nexia processor and so far are happy with it. Sounds good, very flexible. Mostly made for installed systems, but that's how we use it.
23rd July 2014
rongon's Avatar
rongon
diyAudio Member
Great article! I've been re-examining my hifi setup (all DIY tube amplification with store-bought turntable, SACD player and FM tuner). My power amp has very low sensitivity, by home audio standards. It takes about 4V peak input to get to clipping.

I used to use a line preamp with about 12X gain (about 22dB) and output impedance of about 2k ohms. The grid bias on the input was about 4V, able to accommodate the 2.83V peak output from a CD player without distress. At one point, I put the 100k volume control on the output of the preamp, right after the output coupling cap. The wiper went to the RCA output jack. Max output impedance would then be 25k, but power amp's input impedance is about 10x that, at 220k (all of this stuff is vacuum tube).

This idea was criticized for having the preamp run at full tilt into the output level control, which means more distortion from the preamp.

My question is, how is putting the volume control on the output of the preamp different than putting it on the input of the power amp? What are the pros, cons? Or are you recommending using a preamp volume control *and* a power amp input level control, to balance the gain structure to maximize signal to noise ration for your particular setup?

Sorry for changing the subject.

--

Comment


Hide this!Advertise here!
Article Tools Search this Article
Search this Article:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Article Article Starter Category Comments Last Post
help on amp gain structure nicoch58 Tubes / Valves 3 16th December 2010 11:09 PM
S/PDIF data structure billbo Digital Line Level 4 14th October 2008 12:16 PM
6M6G Structure of the circuit RCA245 Tubes / Valves 2 11th April 2005 05:51 PM
Anybody know anything about this kind of motor structure? 454Casull Multi-Way 2 3rd August 2004 12:40 AM


New To Site? Need Help?

All times are GMT. The time now is 02:13 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2