doubling is 3db analog, 6db digital? - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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
Reply
 
Thread Tools Search this Thread
Old 24th March 2011, 09:40 PM   #1
diyAudio Member
 
Join Date: Dec 2010
Default doubling is 3db analog, 6db digital?

Can anyone give me a simple explanation for why doubling the power leads to a 3dBSPL increase, whereas doubling the number of bits in digital audio leads to a 6dBSNR increase? This is confusing because I thought dBs were a dimensionless scale that should work the same no matter what property was being measured.
  Reply With Quote
Old 24th March 2011, 10:10 PM   #2
diyAudio Member
 
Join Date: Dec 2010
After reading this page: How to Calculate the Signal to Noise Ratio | eHow.com I think I have an idea of how to answer my question.

The reason comes down to the different quantities being measured. SPL measures power, but it's the signal level (expressed in Voltage) that doubling bit depth doubles. The relationship between the two is P=V^2/R, or in other words Power is proportional to Voltage squared. That power of 2 is the reason for the 6db digital versus 3db SPL.

Another perhaps simpler way of looking at this is to take an example.
Lets compare two systems:

System A is a 16 bit system with a max voltage of 1 Vrms full scale.
System B is a 17 bit system with a max voltage of 2 Vrms full scale.

Both systems have the same quantization error noise level because they both represent values up to 1 volt with the first 16 bits, exactly the same.

System B doubles the full scale Voltage, and Quadruples the full scale Power (because Power is proportional to 1V squared in System A, and proportional to 2V squared in system B). The effect where a single bit quadruples the power is the reason for the 6db (not 3db) increase per bit in dbSNR for digital.

Yet another thing that helped jog my memory on this is the two formulas:

dB in power terms = 10 log (P1/P2) -> doubling increases by 3db for Power
dB in Voltage terms = 20 log (V1/V2) -> doubling increases by 6db for Voltage
  Reply With Quote
Old 25th March 2011, 01:33 PM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
I have no idea why they adopted the term "power" to specify amplifiers and speakers.
Voltages and currents would have done better and avoided all the confusion that has resulted from power specifications.

I would love to see a speaker specified as being matched up or requiring an amplifier with a 20Vac to 30Vac maximum continuous output.

I would love to see amplifiers specified by their output volts into a range of standard load resistances, eg. 2r0, 4r0, 8r0. And it would be nice to see how long each load can be driven. Better than nice. It would differentiate the good from the bad.
__________________
regards Andrew T.
  Reply With Quote
Old 25th March 2011, 01:58 PM   #4
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
I agree with that point.
It gets even more confusing when trying explain how to drive some thing like an ESL load. jer
  Reply With Quote
Old 25th March 2011, 03:30 PM   #5
diyAudio Member
 
purplepeople's Avatar
 
Join Date: Mar 2003
Location: London, Ontario, Canada
Quote:
Originally Posted by AndrewT View Post
It would differentiate the good from the bad.
And that's the problem. Even people buying cheap gear want to believe they are not getting crap. Maybe not top flight, but not crap. Truly useful specs would force too many manufacturers to decide between making good equipment or marketing crap.

The way it stands, the philosophy remains "caveat emptor".

:)ensen.
__________________
Those who claim to be making history are often the same ones repeating it.
  Reply With Quote

Reply


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

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
Thread Thread Starter Forum Replies Last Post
Woofers working together, +3dB or +6dB? freos Multi-Way 122 24th March 2012 04:50 PM
Analog or digital? rfarn Solid State 0 13th February 2008 04:24 AM
3db increase by doubling driver count Bazukaz Multi-Way 53 17th July 2006 08:30 AM
Doubling Digital Input : Question Blue_Max Digital Source 8 2nd December 2004 07:30 PM
Analog to Digital? Ioannis Digital Source 5 11th December 2001 06:52 PM


New To Site? Need Help?

All times are GMT. The time now is 10:06 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