HomeStudioGuide.com - Guide to Home Studio Recording - What is a decibel... dB, dBm, dBu, dBV, drum n Bass?

Navigation

Home

DIY Projects

DIY-Central Blog

Electronics Bookstore

Home Studio Equipment List

Search

Blogroll

| |

E-mail

Total Posts: 46
This Year: 0
This Month: 0
This Week: 0
Comments: 19

SC-1 Mic Preamp NOW ON SALE!!!!

After many months of development, testing, troubleshooting, frustration, problems, and accomplishments... the SC-1 mic preamp kit, PSU-1848 power supply kit and power transformer kits are now available for sale!

Click here to ORDER

Photo of a finished SC-1 mic preamp kit! (Note: XLR jacks and wires shown on picture not included in the kit.)

Features:
- Low-Noise, transformerless, High-Quality Mic Preamp
- All solid-state design, using chipsets from THAT Corp and Burr-Brown
- Soft-start, slow ramp-on +48V phantom power
- Crystal clear Red LED indicator for phantom power
- Electronically balanced input and output stages
- 12-position Grayhill gain selector switch
- Gain range from +6 to +72dB, in 6dB increments
- Input RFI protection
- Input clamping protection
- Output surge protection circuit
- Output RFI protection
... read more...

Download PDF file of Assembly Guide/Kit Instructions

Related products like the PSU-1848 Power Supply Kit, Power Transformer Kit, Power Control Kit are also available for sale. Click here.

Monday, November 27, 2006

What is a decibel... dB, dBm, dBu, dBV, drum n Bass?

Monday, November 27, 2006 8:56:22 PM (Central Standard Time, UTC-06:00) ( Recording )

The term decibel has been used and abused and thrown around. You go to a music store and the clerk will tell you, "Buy this one instead, it has -10dBu inputs! " Meanwhile, you nod your head... thinking, "this must be better than the 4dBu unit I saw at the HomeStudioGuide.com website, and it's even cheaper...."

prrrrrrrrrrrrttttt!!!

First, let's understand what the word "decibel" really means.

In simple terms, decibel denotes or describes the ratio of two numbers. The reason why "decibel" is used is because it's logarithmic, and therefore you can represent extremely large ratios using smaller numbers. Also, our human ears respond "logarithmically" so dB values translate better how we hear things, than absolute number ratios.

decibel is actually 1/10th of a Bel. From the root word "deci" which means 10, and Bel (named after Alexander Graham Bell, the inventor of the telephone.) WHAT!!!!   What does the telephone have to do with making music? (other than those cheesy voice sound effects on the telephone)

A Bel is the logarithm of a ratio. i,e. Power Ratio.

in math, this is expressed as Bel = log (P1/P0)

Since we're talking decibel instead of Bel, the formula is

decibel (Power) = 10 x log (P1/P0)     ; where P1,P0 are power values (i.e. watts)

REMEMBER THIS: A decibel does not describe the power value/reading/number itself, but the RATIO between two powers.

Example #1: If you have an amplifier that increases an input of 1watt to 2 watts (i.e. doubles it), using the formula above, we can say that the amplifier has a 3dB power gain.

Example #2: If you have an amplifier that increases an input of 10 watts to 100 watts output, what is the dB gain of that amplifier? The answer is 10dB.

Rule of thumb = if you DOUBLE the POWER, then you increase it by 3dB
Rule of thumb = if you HALVE the POWER, then you decrease it by 3dB

* Note, it doesn't matter if it's doubling from 1 watt to 2 watts, or 100 watts to 200 watts, they're both an increase of 3dB.

Rule of thumb = if you increase the POWER by TEN times, then you increase it by 10dB
Ruel of thumb = if you decreate the POWER to 1/10th of it's original power, then you decrease it by -10dB

* Note: Again, increasing power from 100 watts to 1Kwatts (or 1,000 watts) is still a 10dB increase, the same if you increase 10 watts to 100 watts, it's still a 10dB increase.

Notice a pattern here? The actual output power, 1,000 watts or 100 watts doesn't matter. What matters is the ratio of the 2 numbers... in our example, 1,000 watts and 100 watts.   OR 100 watts and 10 watts.

Keep in mind....decibel is a RATIO.

Now.... here's where it gets a little complicated (if you don't know Ohms Law and Power calculations). So try to follow me, okay?

Power is proportional to the square of the voltage. In Ohm's Law, this is represented as P = (E x E) / R   ; where E=voltage, and R=resistance in ohms

So if we're going to be talking about decibels as it applies to VOLTAGE (instead of POWER like what we did in the above example), then we change the formula of decibel as follows:

decibel(Volts) = 20 log (E1/E0) ; where E1 and E0 are voltage readings (i.e. volts)

okay, still with me? You know how we said earlier that DOUBLE the POWER is the same as increasing it by 3dB.

This time, DOUBLE the VOLTAGE is the same as increasing it by 6dB.

Earlier we said TEN TIMES the POWER is the same as increasing it by 10dB.

This time, TEN TIMES the VOLTAGE is the same as increasing it by 20dB.

Earlier I said that the beauty of decibel is the ability to describe the large ratios of two numbers using a small value.

In POWER, (assuming a reference level of 1 watt; i.e. the denominator in our ratio, i.e. the bottom number), a 100,000 watts compared to 1 watt reference number can be described as 50dB.

Power Ratio (watts) = dB reading
1 = 0
10 = 10
100 = 20
200 = 23
400 = 26
800 = 29
1000 = 30
2000 = 33
4000 = 36
8000 = 39
10000 = 40
20000 = 43
40000 = 46
80000 = 49
100,000 = 50

Notice that going from 1000 watts to 2000 watts is just an increase of 3dB? from 30dB to 33dB?
Also notice that going from 40,000 watts to 80,000 watts is ALSO an increase of 3dB? from 46dB to 49dB?

Don't forget... for POWER, everytime you double it, you increase the dB by 3.
For VOLTAGE, everytime you double it, you increase the dB by 6.

Click here for continuation...

Comments [1] | Trackback |

HomeStudioGuide.com - Guide to Home Studio Recording

Guide to Recording, Mixing, Mastering, DIY, PCB Designs, etc.

Navigation

Search

On this page

Archive

Blogroll