audacity-devel

 [Audacity-devel] 24-bit audio and plot spectrum From: Doc Nelson - 2009-03-26 01:56:07 ```Martyn Shaw wrote: > Sorry, this is only half a post, but I am a bit inundated right now... > > Doc Nelson wrote: >> During testing for 24 bit operation, I encountered a Plot Spectrum >> with a purple screen, the usual -90dB at bottom but -102 at the top. >> >> To determine what triggers this, I made a tone of 4410 Hz with 0dB >> amplitude (using Generate with amplitude of 1 makes a signal at >> -.4dB, so an amplify of .4 pushes it to full amplitude. Close >> inspection did not reveal any clipping. > > This is bogus. You made a signal with 10 samples per cycle, and a > sinewave, so the first maximum occurs at 360/4 = 90 degrees but that > doesn't correspond with a sample. The samples are at 360/10 degrees > so the 1st max ones are at 72 and 108 degrees. > 20*log10(sin(72degrees)) = -0.436 dB. If you were to upsample (and so > fill in the gaps) (Tracks -> Resample... -> 96000 (eg)) then there > would be values exceeding 1. Recent changes have meant that they > don't get clipped internally, but you may not have that version. OK, you're right. I was a bit lazy and wanted an integer divison, so 10 was conveniently done in head. I'll run the experiment again dividing by 8 or 12. I'll set the sampling rate to 48k to make arithmentic simple > >> Amplify -96dB does not work -- it produces a signal of about -48. > > We restrict 'Amplify' to a maximum of 50dB per application (I don't > know why). No big deal. It's probably only for rare testing like this that anybody would want to make attenuations greater than 50dB. Still, the why is a good question. Why not just let it go to -144dB?? > > I'm going to have to get back to you on the rest... Thanks for the help. I have learned a lot about Audacity and the team's good works. I would really like to do a bit of code development, but have to confess I am intimidated by the complexity of the OS environments and tools and methods. Would it be useful to document any of this for a tutorial? I had a friend/professional software developer do the ALSA build that you tutored in the past. He has since moved away and I have lost the recipe. > > TTFN > Martyn > >> Accordingly, I applied Amplify -48 twice to get a test tone at -96dB. >> At that level Plot Spectrum (4096) works as usual showing a peak >> signal at 4410Hz with amplitude of -86.7. The vertical scale of the >> plot differs significantly from the measured values from the cursor. >> This result is solidly repeatable -- no variations over several tests. >> >> I next applied Amplify -6dB repeatedly until the Plot Spectrum screen >> went purple. At a level of -114dB the Plot Spectrum still operates as >> usual, but there is no signal displayed. At -117 the purple screen >> appears. >> >> I also made some measurements of this test tone at 0dB, -24dB, -48dB, >> -72dB and -96dB for FFT widths from 128 to 4096 samples. >> >> In all cases, the level indication of the Output Playback Meter >> precisely matches the sinusoidal peak amplitude so there is no >> attempt to apply square roots of 2 for RMS or fudge factors to >> convert to dBU. The output meter scale is dBV peak. >> >> Cursor-measured spectrum peaks tracked the 24dB attenuations of the >> signal. At each level, I measured the peak at several FFT widths and >> find the the cursor-measured peak drops by approximately 3dB for each >> halving of the FFT width from 4096 down to 128 samples. But that >> number varies quite predictably as follows 3.7dB, 2.8dB, 3dB, 2.6dB, >> and 3.5dB as we go from 128 to 256 to 512 to 1024 to 2048 to 4096 >> samples at all signal levels. >> >> Apparently the tool scales results by the square root of the >> bandwidth producing results in dB/rootHz. My HP audio spectrum >> analyzer has that feature as an option. We might want to make that >> correction optional by a setting in Preferences/Spectrograms. >> >> Suggestions: >> I suggest that the Preferences/Spectrograms wants to have a feature >> like Preferences/Interface so users can choose to have the spectrum >> vertical scale go down below the noise floor of their 24-bit sampler. >> There is some logic to having the spectrum analyzer inherit the >> selection from Preferences/Interface. It also seems as if we ought to >> have the vertical scale of the graph match the calibration of the >> cursor measurements. The differences are in many cases quite large. I >> did not attempt to quantify once it was clear that the cursor was >> entirely reliable. >> >> Questions: >> I would very much like to know what the Plot Spectrum does when we >> select a patch of signal longer the the 2^N FFT width. Does it take >> the 2^N samples from the left edge, right edge, average several >> spectra across entire window or what? >> >> Are we using the FFTW freeware from MIT? http://www.fftw.org/ >> >> Thanks >> > > -- Gary Nelson Porpoise Research Institute Port Townsend, WA, 98368 -- Gary Nelson Porpoise Research Institute Port Townsend, WA, 98368 ```
 Re: [Audacity-devel] 24-bit audio and plot spectrum From: sherone - 2009-03-26 06:08:53 ``` Martyn Shaw wrote: > Sorry, this is only half a post, but I am a bit inundated right now... > > Doc Nelson wrote: >> During testing for 24 bit operation, I encountered a Plot Spectrum >> with a purple screen, the usual -90dB at bottom but -102 at the top. >> >> To determine what triggers this, I made a tone of 4410 Hz with 0dB >> amplitude (using Generate with amplitude of 1 makes a signal at >> -.4dB, so an amplify of .4 pushes it to full amplitude. Close >> inspection did not reveal any clipping. > > This is bogus. You made a signal with 10 samples per cycle, and a > sinewave, so the first maximum occurs at 360/4 = 90 degrees but that > doesn't correspond with a sample. The samples are at 360/10 degrees > so the 1st max ones are at 72 and 108 degrees. > 20*log10(sin(72degrees)) = -0.436 dB. If you were to upsample (and so > fill in the gaps) (Tracks -> Resample... -> 96000 (eg)) then there > would be values exceeding 1. Recent changes have meant that they > don't get clipped internally, but you may not have that version. OK, you're right. I was a bit lazy and wanted an integer divison, so 10 was conveniently done in head. I'll run the experiment again dividing by 8 or 12. I'll set the sampling rate to 48k to make arithmentic simple > >> Amplify -96dB does not work -- it produces a signal of about -48. > > We restrict 'Amplify' to a maximum of 50dB per application (I don't > know why). No big deal. It's probably only for rare testing like this that anybody would want to make attenuations greater than 50dB. Still, the why is a good question. Why not just let it go to -144dB?? > > I'm going to have to get back to you on the rest... Thanks for the help. I have learned a lot about Audacity and the team's good works. I would really like to do a bit of code development, but have to confess I am intimidated by the complexity of the OS environments and tools and methods. Would it be useful to document any of this for a tutorial? I had a friend/professional software developer do the ALSA build that you tutored in the past. He has since moved away and I have lost the recipe. > > TTFN > Martyn > >> Accordingly, I applied Amplify -48 twice to get a test tone at -96dB. >> At that level Plot Spectrum (4096) works as usual showing a peak >> signal at 4410Hz with amplitude of -86.7. The vertical scale of the >> plot differs significantly from the measured values from the cursor. >> This result is solidly repeatable -- no variations over several tests. >> >> I next applied Amplify -6dB repeatedly until the Plot Spectrum screen >> went purple. At a level of -114dB the Plot Spectrum still operates as >> usual, but there is no signal displayed. At -117 the purple screen >> appears. >> >> I also made some measurements of this test tone at 0dB, -24dB, -48dB, >> -72dB and -96dB for FFT widths from 128 to 4096 samples. >> >> In all cases, the level indication of the Output Playback Meter >> precisely matches the sinusoidal peak amplitude so there is no >> attempt to apply square roots of 2 for RMS or fudge factors to >> convert to dBU. The output meter scale is dBV peak. >> >> Cursor-measured spectrum peaks tracked the 24dB attenuations of the >> signal. At each level, I measured the peak at several FFT widths and >> find the the cursor-measured peak drops by approximately 3dB for each >> halving of the FFT width from 4096 down to 128 samples. But that >> number varies quite predictably as follows 3.7dB, 2.8dB, 3dB, 2.6dB, >> and 3.5dB as we go from 128 to 256 to 512 to 1024 to 2048 to 4096 >> samples at all signal levels. >> >> Apparently the tool scales results by the square root of the >> bandwidth producing results in dB/rootHz. My HP audio spectrum >> analyzer has that feature as an option. We might want to make that >> correction optional by a setting in Preferences/Spectrograms. >> >> Suggestions: >> I suggest that the Preferences/Spectrograms wants to have a feature >> like Preferences/Interface so users can choose to have the spectrum >> vertical scale go down below the noise floor of their 24-bit sampler. >> There is some logic to having the spectrum analyzer inherit the >> selection from Preferences/Interface. It also seems as if we ought to >> have the vertical scale of the graph match the calibration of the >> cursor measurements. The differences are in many cases quite large. I >> did not attempt to quantify once it was clear that the cursor was >> entirely reliable. >> >> Questions: >> I would very much like to know what the Plot Spectrum does when we >> select a patch of signal longer the the 2^N FFT width. Does it take >> the 2^N samples from the left edge, right edge, average several >> spectra across entire window or what? >> >> Are we using the FFTW freeware from MIT? http://www.fftw.org/ >> >> Thanks >> > > -- Gary Nelson Porpoise Research Institute Port Townsend, WA, 98368 -- Gary Nelson Porpoise Research Institute Port Townsend, WA, 98368 ------------------------------------------------------------------------------ _______________________________________________ audacity-devel mailing list audacity-devel@... https://lists.sourceforge.net/lists/listinfo/audacity-devel your wall speakers may not be connected.... disconnect each speaker from the selector box and test with a small AAA battery to see if they are connected by putting the battery between each speaker's wires , you will hear it crackle ,then gradually connect each wall speaker onto the speaker connector box . If the first set does not work i suggest there may be a problem with your speaker selector box . Best of luck ----- http://www.download-audacity.co.cc Download Audacity -- View this message in context: http://n2.nabble.com/24-bit-audio-and-plot-spectrum-tp2536138p2536803.html Sent from the audacity-devel mailing list archive at Nabble.com. ```
 Re: [Audacity-devel] 24-bit audio and plot spectrum From: Martyn Shaw - 2009-04-15 23:13:07 ```Hi Doc Nelson I just updated the Frequency Analysis window to use the Interface preference as the minimum on the vertical scale. This enables you to plot spectrums down to -145 dB if you are using that scale for the meters etc. I think you'll find it an improvement. What with that and the optional grids, corrections for the width of the windows and new 'Replot' button I think all of you plotting problems have been solved (?). I know that Gale is still doing very recent builds and putting them up at http://www.gaclrecords.org.uk/audacity.html (Windows latest development build) so you should be able to get a copy of this in the next day or so. Does anyone think that the minimum on the vertical scale on 'Analyse -> Plot Spectrum...' should change if you have a small meter range selected in 'Prefs -> Interface -> Meter/Waveform dB range:'? I've set the minimum to at least -90dB, as it was before. It now only changes if the meter range is larger. Also, should we rename 'Meter/Waveform dB range:' in prefs as 'dB range:'? Also in audacity.cfg, should it be 'dBRange' now, rather than 'EnvdBRange'? There are historical reasons for the naming, I'm sure, but it has gone beyond that. TTFN Martyn Doc Nelson wrote: > Martyn Shaw wrote: >> Sorry, this is only half a post, but I am a bit inundated right now... >> >> Doc Nelson wrote: >>> During testing for 24 bit operation, I encountered a Plot Spectrum >>> with a purple screen, the usual -90dB at bottom but -102 at the top. >>> >>> To determine what triggers this, I made a tone of 4410 Hz with 0dB >>> amplitude (using Generate with amplitude of 1 makes a signal at >>> -.4dB, so an amplify of .4 pushes it to full amplitude. Close >>> inspection did not reveal any clipping. >> This is bogus. You made a signal with 10 samples per cycle, and a >> sinewave, so the first maximum occurs at 360/4 = 90 degrees but that >> doesn't correspond with a sample. The samples are at 360/10 degrees >> so the 1st max ones are at 72 and 108 degrees. >> 20*log10(sin(72degrees)) = -0.436 dB. If you were to upsample (and so >> fill in the gaps) (Tracks -> Resample... -> 96000 (eg)) then there >> would be values exceeding 1. Recent changes have meant that they >> don't get clipped internally, but you may not have that version. > OK, you're right. I was a bit lazy and wanted an integer divison, so 10 > was conveniently done in head. I'll run the experiment again dividing by > 8 or 12. I'll set the sampling rate to 48k to make arithmentic simple >>> Amplify -96dB does not work -- it produces a signal of about -48. >> We restrict 'Amplify' to a maximum of 50dB per application (I don't >> know why). > No big deal. It's probably only for rare testing like this that anybody > would want to make attenuations greater than 50dB. Still, the why is a > good question. Why not just let it go to -144dB?? >> I'm going to have to get back to you on the rest... > Thanks for the help. I have learned a lot about Audacity and the team's > good works. > > I would really like to do a bit of code development, but have to confess > I am intimidated by the complexity of the OS environments and tools and > methods. Would it be useful to document any of this for a tutorial? > > I had a friend/professional software developer do the ALSA build that > you tutored in the past. He has since moved away and I have lost the > recipe. >> TTFN >> Martyn >> >>> Accordingly, I applied Amplify -48 twice to get a test tone at -96dB. >>> At that level Plot Spectrum (4096) works as usual showing a peak >>> signal at 4410Hz with amplitude of -86.7. The vertical scale of the >>> plot differs significantly from the measured values from the cursor. >>> This result is solidly repeatable -- no variations over several tests. >>> >>> I next applied Amplify -6dB repeatedly until the Plot Spectrum screen >>> went purple. At a level of -114dB the Plot Spectrum still operates as >>> usual, but there is no signal displayed. At -117 the purple screen >>> appears. >>> >>> I also made some measurements of this test tone at 0dB, -24dB, -48dB, >>> -72dB and -96dB for FFT widths from 128 to 4096 samples. >>> >>> In all cases, the level indication of the Output Playback Meter >>> precisely matches the sinusoidal peak amplitude so there is no >>> attempt to apply square roots of 2 for RMS or fudge factors to >>> convert to dBU. The output meter scale is dBV peak. >>> >>> Cursor-measured spectrum peaks tracked the 24dB attenuations of the >>> signal. At each level, I measured the peak at several FFT widths and >>> find the the cursor-measured peak drops by approximately 3dB for each >>> halving of the FFT width from 4096 down to 128 samples. But that >>> number varies quite predictably as follows 3.7dB, 2.8dB, 3dB, 2.6dB, >>> and 3.5dB as we go from 128 to 256 to 512 to 1024 to 2048 to 4096 >>> samples at all signal levels. >>> >>> Apparently the tool scales results by the square root of the >>> bandwidth producing results in dB/rootHz. My HP audio spectrum >>> analyzer has that feature as an option. We might want to make that >>> correction optional by a setting in Preferences/Spectrograms. >>> >>> Suggestions: >>> I suggest that the Preferences/Spectrograms wants to have a feature >>> like Preferences/Interface so users can choose to have the spectrum >>> vertical scale go down below the noise floor of their 24-bit sampler. >>> There is some logic to having the spectrum analyzer inherit the >>> selection from Preferences/Interface. It also seems as if we ought to >>> have the vertical scale of the graph match the calibration of the >>> cursor measurements. The differences are in many cases quite large. I >>> did not attempt to quantify once it was clear that the cursor was >>> entirely reliable. >>> >>> Questions: >>> I would very much like to know what the Plot Spectrum does when we >>> select a patch of signal longer the the 2^N FFT width. Does it take >>> the 2^N samples from the left edge, right edge, average several >>> spectra across entire window or what? >>> >>> Are we using the FFTW freeware from MIT? http://www.fftw.org/ >>> >>> Thanks >>> >> > > ```