# Noisy source block **URL:** \ **Category:** GNU Radio\ **Created:** [April 15, 2014, 5:19am UTC](https://www.ruby-forum.com/t/noisy-source-block/240453 "2014-04-15T05:19:54Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [April 15, 2014, 5:19am UTC](https://www.ruby-forum.com/t/noisy-source-block/240453/1 "2014-04-15T05:19:54Z")
higuys why the unit of amplitude in Noisy source block is volt? how to explain this ? thanks, BZS ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 15, 2014, 10:32am UTC](https://www.ruby-forum.com/t/noisy-source-block/240453/2 "2014-04-15T10:32:31Z")
On 04/15/2014 04:46 AM, 猪猪猪猪猪猪头 wrote: > hi，guys > why the unit of amplitude in Noisy source block is volt? > how to explain this ? > thanks, > BZS Not sure what your question is. Signal amplitudes are usually in Volts, that’s just the right physical unit. I assume you’re asking because in the digital domain, there’s really no volts, and that’s a good point. The unit could also just be 1. This is something you sometimes see in (especially older) DSP textbooks. There’s a similar thing, where the mag-square of a signal is often considered its instantaneous power (which, would assume a resistance of 1 \Ohm if you’re still thinking in physical power). So, just ignore this if it confuses you. Martin ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 15, 2014, 12:06pm UTC](https://www.ruby-forum.com/t/noisy-source-block/240453/3 "2014-04-15T12:06:55Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi 猪猪猪猪猪猪头, you’ve replied to the wrong thread; however: dB is _always_ a relative measure. You can’t output dB; it always has to be dB in relation to something. The parameter of the noise source is amplitude. Like Martin, if I _want_ to stick a physical entity to it, it would be voltage. Usually, I don’t – the noise source just outputs a realization of a complex random process; it’s just numbers without unit. I’m under the impression you’re mixing up absolute noise power, noise variance, and SNR; for SNR, which is a ratio, dB does indeed make sense. However, you don’t get a noise source that generates a certain SNR, because that depends on the signal power, and is something that you/your application has to calculate. Greetings, Marcus > hi ,Martin B. well ,in my impression, the unit of is noisy is > dB,so i feel fuzzy > about the volt, > thanks for your reply! -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTTQRbAAoJEBQ6EdjyzlHtxuAH/ieCgneEsA7ET+lUl28SEhXq AaMa0Zv0Idrg4FKOudkDeydcUVL6sTPwAkEKjVxfdQ1bkDJp2gWg2IPMd1KadQI4 I46YLa5tIx44dRD481BXg+MCSHibYzwvqNdGzX5bB2YXUFSMN7SWq9kZm70074Wx 3yRMPxC+r7bISuN66m10NrcElo7eFsB+6dpNNoOITCwIe7xrhLfGUJ4H4TNp2LQM EUki7ELRO6lgz7vHKdjkrTUPb2i9JhRIuCd6gZlfgz/1qms8n6pUxLVoQj2dRS7Q 7R6cEvwd8tLuwt6h9BIuK0twttYXRqedpHxgSyqGcNopLQHFg7IeIlSqAZideYM= =9w3p -----END PGP SIGNATURE-----