## audacity-users

 [Audacity-users] meters From: - 2005-11-24 23:39:17 ```I was playing a tone file through Audacity 1.2.3 to try to figure out how the levels are indicated on the meters. I exploded the sound file image as well in the window. It was not a very loud tone. When I exploded the view, it showed me about +/-0.088 at the peaks of the tone waveforem which was a 1kHz tone. I assume the 0.088 is a the portion of full scale as the scales end at +/-1. The meters when I undocked them and spread it out across my entire screen was showing -21dB at the far right end where the dark green bar ends, and about - 36.8dB at the left end of the dark green portion. Bright green of course extends leftward to the end. So here is my question: What is full scale in terms of voltage or power? And if the answer is in power, what is the assumed impedance? I converted the 0.088 to -21dB using 20LOG0.088 so I am thinking the -21 point is peak. But what does the ~-37dB point mean, and what is full scale? Thanks! Robert. ```
 Re: [Audacity-users] meters From: chris319 - 2005-11-27 02:32:47 ```>What is full scale in terms of voltage or power? This is purely a function of your sound card. The program or a sound file only know about digital values from -32768 to 32767 in the case of 16-bit samples. The output voltage depends on the amount of amplification the analog signal receives after it comes out of the sound card's DAC. ```
 Re: [Audacity-users] meters From: - 2005-11-28 20:09:48 ```Thanks for the reply Chris: I agree the final output of something like a soundcard is going to vary wildly. I also agree with your conversion limits of +/-32768. However, I have to believe that there is a real world analog equivalent to a digital signal measurement. Every piece of equipment out there, when confronted with a digital signal that measures XdB digitally (- 21dB peak in my case), needs to be able to convert that signal to analog and then present that signal to whatever amplifier is there. So my original question still stands. There has to be an equivalent analog level for a digital signal. If a signal were to measure exactly 0dB full scale on the Audacity meters, what is its' real world equivalent analog measurement, before any amplifiers are involved? Regards, Robert. Quoting chris319 : > >What is full scale in terms of voltage or power? > > This is purely a function of your sound card. The program or a sound file > only know about digital values from -32768 to 32767 in the case of 16-bit > samples. The output voltage depends on the amount of amplification the > analog > signal receives after it comes out of the sound card's DAC. > > > > ------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files > for problems? Stop! Download the new AJAX search engine that makes > searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! > http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click > -- > Mailing list: Audacity-users@... > To UNSUBSCRIBE, use the form at the bottom of this web page: > https://lists.sourceforge.net/lists/listinfo/audacity-users > ```
 Re: [Audacity-users] meters From: chris319 - 2005-11-29 05:42:50 ```> -----Original Message----- > From: rfuller@... [mailto:rfuller@...] > Sent: Monday, November 28, 2005 08:09 PM > To: audacity-users@..., 'chris319' > Subject: Re: [Audacity-users] meters > > I have to believe that there is a real world analog > equivalent to a digital signal measurement. Every piece of equipment out > there, when confronted with a digital signal that measures XdB digitally (- > 21dB peak in my case), needs to be able to convert that signal to analog and > then present that signal to whatever amplifier is there. There is no analog equivalent to any digital value. Going back to first principles, dB is not an absolute unit of measurement, but rather it expresses a ratio, usually to some reference. In the digital audio realm the reference is all bits in the sample equal to one. In a 16-bit sample this is 32767 (one bit is a sign bit). Every time a most-significant bit is dropped, the level is reduced by 6 dB. The output voltage depends on what the DAC puts out and how the designers of a piece of equipment amp up that output. Also consider that a in a properly-designed piece of equipment, a 16-bit sample at 0 dBFS will put out the same analog level as a 24-bit sample, and the noise floor of the latter will be lower. ```
 Re: [Audacity-users] meters From: - 2005-11-29 06:14:18 ```Chris has hit the nail on the head. What I am asking I guess is...what is the reference. It is exactly right that dB is ALWAYS referred to something. So another a way for me to ask my question is not to say is this dBV or dBu, but what is the reference? I have two completely independent programs (Audacity being one of them) that give me the same -21dB peak. So what is this -21 referred to. I can hear people out there saying "it is referred to full scale" But fullscale must mean something. What is fullscale. If multiple programs can come up with the exact same -21dB value, there must be some standard to which it is referred? Regards, Robert. ```
 Re: [Audacity-users] meters From: chris319 - 2005-11-29 13:56:59 ```>another a way for me to ask my question is not to say is this dBV or dBu, >but what is the reference? I already answered this: >In the digital audio realm the reference is all bits in the sample equal >to one. In a 16-bit sample this is 32767 (one bit is a sign bit). Every >time a most-significant bit is dropped, the level is reduced by 6 dB. In binary notation it would be Sign bit->0 111111111111111 = +32767 or full-scale positive excursion Sign bit->1 111111111111111 = -32768 or full-scale negative excursion ```
 Re: [Audacity-users] meters From: - 2005-11-30 02:11:53 ```OK so I figured this out through another board. Thought I would post the answer here for anyone who wishes to debate it further. Audacity and Cool Edit and others all deflect their meters the same amount to the signal of interest. So there has to be a common reference. It just needed to be found. The experiment was more complicated than what I am about to type, but in the interest of brevity, here 'goes. By injecting a known signal digitally into the stream I was measuring, then stripping that signal out of that same stream and converting it too a .au audio file I was able to play it through Audacity. The meter deflected to -19dBpk. First of all, it took some time to figure out how to get a digital signal injected that I could trust implicitly. But now that I have that, I can move on. So the question was, dB?what? By converting the measurement to rms you get - 22dBrms. The known signal was -16dBu. So simple subtration shows a difference of exactly +6dB of signal unaccounted for in the measurement. So full scale in Audacity and at least three other programs is +6dBu. From there converting to any other known quantity like dBV or others is a piece of cake. Thus the reference is found. I don't think Im wrong... But maybe... Comments... Regards, Robert. Quoting chris319 : > >another a way for me to ask my question is not to say is this dBV or dBu, > >but what is the reference? > > I already answered this: > > >In the digital audio realm the reference is all bits in the sample equal > >to one. In a 16-bit sample this is 32767 (one bit is a sign bit). Every > >time a most-significant bit is dropped, the level is reduced by 6 dB. > > In binary notation it would be > > Sign bit->0 111111111111111 = +32767 or full-scale positive excursion > > Sign bit->1 111111111111111 = -32768 or full-scale negative excursion > > > > ------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. Do you grep through log files > for problems? Stop! Download the new AJAX search engine that makes > searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! > http://ads.osdn.com/?ad_id=7637&alloc_id=16865&op=click > -- > Mailing list: Audacity-users@... > To UNSUBSCRIBE, use the form at the bottom of this web page: > https://lists.sourceforge.net/lists/listinfo/audacity-users > ```
 Re: [Audacity-users] meters From: Phil Nelson - 2005-11-29 05:07:41 ```If I may jump in here, this might help: http://www.rane.com/par-d.html Try scrolling down do "decibel" on that page. As you can see there, not only is there "an equivalent analog level", there are several of them! Phil Nelson rfuller@... wrote: > Thanks for the reply Chris: I agree the final output of something like a > soundcard is going to vary wildly. I also agree with your conversion limits of > +/-32768. However, I have to believe that there is a real world analog > equivalent to a digital signal measurement. Every piece of equipment out > there, when confronted with a digital signal that measures XdB digitally (- > 21dB peak in my case), needs to be able to convert that signal to analog and > then present that signal to whatever amplifier is there. > So my original question still stands. There has to be an equivalent analog > level for a digital signal. If a signal were to measure exactly 0dB full scale > on the Audacity meters, what is its' real world equivalent analog measurement, > before any amplifiers are involved? > > Regards, > > Robert. > > > > Quoting chris319 : > > >>> What is full scale in terms of voltage or power? >>> >> This is purely a function of your sound card. The program or a sound file >> only know about digital values from -32768 to 32767 in the case of 16-bit >> samples. The output voltage depends on the amount of amplification the >> analog >> signal receives after it comes out of the sound card's DAC. >> >> >> ```
 Re: [Audacity-users] meters From: Shinano Sato - 2005-11-29 05:32:49 ``` Thanks But I am busy. Shinano Sato On 11/29/05, Phil Nelson wrote: > > If I may jump in here, this might help: http://www.rane.com/par-d.html > > Try scrolling down do "decibel" on that page. As you can see there, not > only is there "an equivalent analog level", there are several of them! > > Phil Nelson > > rfuller@... wrote: > > Thanks for the reply Chris: I agree the final output of something like = a > > soundcard is going to vary wildly. I also agree with your conversion li= mits of > > +/-32768. However, I have to believe that there is a real world analog > > equivalent to a digital signal measurement. Every piece of equipment ou= t > > there, when confronted with a digital signal that measures XdB digitall= y (- > > 21dB peak in my case), needs to be able to convert that signal to analo= g and > > then present that signal to whatever amplifier is there. > > So my original question still stands. There has to be an equivalent ana= log > > level for a digital signal. If a signal were to measure exactly 0dB ful= l scale > > on the Audacity meters, what is its' real world equivalent analog measu= rement, > > before any amplifiers are involved? > > > > Regards, > > > > Robert. > > > > > > > > Quoting chris319 : > > > > > >>> What is full scale in terms of voltage or power? > >>> > >> This is purely a function of your sound card. The program or a sound f= ile > >> only know about digital values from -32768 to 32767 in the case of 16-= bit > >> samples. The output voltage depends on the amount of amplification the > >> analog > >> signal receives after it comes out of the sound card's DAC. > >> > >> > >> > > > > ------------------------------------------------------- > This SF.net email is sponsored by: Splunk Inc. Do you grep through log fi= les > for problems? Stop! Download the new AJAX search engine that makes > searching your log files as easy as surfing the web. DOWNLOAD SPLUNK! > http://ads.osdn.com/?ad_id=3D7637&alloc_id=3D16865&op=3Dclick > -- > Mailing list: Audacity-users@... > To UNSUBSCRIBE, use the form at the bottom of this web page: > https://lists.sourceforge.net/lists/listinfo/audacity-users > ```