Decibels (db's)

[pwdrive]

I was not impressed at all!

For a start, I found his style of delivery annoying and distracting. The section where he had 3 amplifiers in cascade and was talking about the 'gain' of each of those stages was very poor: he made no reference to whether the dBs he was referring to were voltage dBs or power dBs. He equated 'magnitudes' to a voltage or a current, but, by implication, not power. Technically then, he is incorrect: a 'magnitude' refers to a size of 'something': that 'something' could be a voltage, current, power, resistance - anything. When he was discussing frequency response of an amplifier, he kept referring to the frequency axis in units of dBs! He also made no reference to source and load resistances and that they often need to be taken into consideration when making dB calculations. There was also various other errors, but these come into the category of hair-splitting, so I have made no reference to them (not wishing to start an argument here! )

But overall, his biggest mistake was his failure to point out, right at the beginning of his 'lecture', that dBs are fundamentally a measure of the ratio of two powers and that using dBs to compare two voltages (or currents) can indeed be done, and indeed is, but when that is done, great care is required.

To me, I feel that anyone who is confused about 'dBs' and then watches that is going to be even more confused by the time they've reached the end of it (and then taken a deep breath! ). Overall I feel that I could have done a much better job.

Al. / Aug. 20, 2013 //

He did actually refer to voltage at the beginning of his explanation of those three amplifier stages.

He did show the difference in the formulas between V (or I) and power when converting to db's

He emphasized earlier on the that db's was just an expression of a ratio, to me that's all db's is.

He explained why using a logarithmic scale has it's advantages in magnitude terms for the Y axis and the X axis as per the spectrum display.

I personally think he initially used the term db's in the X axis purely to illustrate the advantages of displaying time as an order of magnitude which reinforced his early explanation the db's is a ratio, he then clearly went on then to show that order of magnitude in real numbers relating to time/frequency.

That for me was the essence of his presentation, it's just a ratio.

Yes suffixes have to be assigned and I am sure he did mention that somewhere.
It was a simplified explanation and he did not try to hide that fact, like he said it's just a ratio, it could be as a sound pressure level that we can hear or voltage/current/power that we cannot see.

As to his style, I can see he's not going to be everyones cup o' tea, that was my initial response when I first clocked one of his videos as I said previously, however I found his explanation ok and on a level I could relate to....despite his squeaky voice.

Lawrence.