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Title: Analog signal levels Post by: ivo on January 11, 2012, 09:42:40 am Hi folks,
I am not so knowledgeable in decibels and other stuff, so will you please help me out in understanding the specs of my DAC's analog input and output: Line Input / Output Type: Unbalanced RCA Level: -10dBV Nominal (@-16dBFS) / +8dBV max Impedance: 15kΩ(Input) / 200Ω(Output) I want to understand what is the max value in volts (RMS) I can input into 'Line Input'? Also, as the device acts also as pre-amp, I want to know what is the max value again in volts (RMS) to which it actually amplifies? Can I input 2V (RMS) into such Line Input? Thank you and below is the link to orig specs: http://www.audiotrack.net/products/DRDAC2DX/spec/ Ivo Title: Re: Analog signal levels Post by: CoenP on January 11, 2012, 08:24:10 pm I don't know what dBV is referenced to but dBU is 0.775 Volt RMS (about 1 Volt peak). I take it that the spec is incorrectly edited or has been mistyped..
dBFS is full scale, so the nominal value is 16 dB below full scale, which is 10dBV below 1dBU. Iow maximum scale is 16-10 dB = +6dBU or 2x 0.775 V RMS (x0.70707 for Peak Voltage). Peak input would then be slightly more than 2 Volts. On the output side the dac peaks at +8 dBU or 20x log( 8 ) x 0.775 Volt Rms (x0.70707 for the peak value). Any calculator can give you the answer to this :-). [I edited above line so the log( 8 ) doesn't turn into log(8). - Peter] Looks like a quite normal device to me. Regards, Coen Title: Re: Analog signal levels Post by: ivo on January 11, 2012, 08:49:11 pm Thanks Coen! It helps.
Ivo Title: Re: Analog signal levels Post by: CoenP on January 12, 2012, 09:27:56 pm Ok!
i noticed a slight mistake. The peak value is of course 2X 0.70707 = 1.41414 the rms value (square root of 2). Maybe i should try harder to quit listening to the nos1 late night ;) and go to bed at a decent time. Man thats hard! Regards, Coen Title: Re: Analog signal levels Post by: PeterSt on January 13, 2012, 11:22:40 am Quote i noticed a slight mistake. The peak value is of course 2X 0.70707 = 1.41414 the rms value (square root of 2). Or ... or that is the Peak-Peak value. Haha. Anyway, calculations are always performed with the 1.414, so this (p-p) is the comfortable one I think. Peter Title: Re: Analog signal levels Post by: CoenP on January 13, 2012, 04:59:09 pm Well,
Rms value is 0.70707 x the peak value of the sine or in reverse: peak is 1.4141 times the rms. So peak-peak would equate to +1.4141 - - 1.4141 = 2.8283 times the rms. p-p is not of interest when using a dac, rms and peak are all you need. (it can be handy in designing a dac though.) Pffew, I think I made it :)! Regards, Coen Title: Re: Analog signal levels Post by: PeterSt on January 13, 2012, 05:41:14 pm Oh, but you already made it. :)
But the mistakes are so easy to make (at least I have difficulties with it; somewhere another topic on the same floats around). For a differentially setup DAC there's plus and minus voltage throughout. When the balanced output is 2VRMS the peak value of that is 2.828V (see the confusement coming ?). Well, if only plus is supposed to create that. But minus counts too. So, only half of that can do the trick, which is 1.414. Can you still follow ? I already can't without real thinking, and this is because all the nice numbers (like 1.414) always end up like that. So I better grab my second beer; it helps me to forget ... haha |