Re: [slim] Re: Spectrum Analyzer reversed?
A.J. Aranyosi wrote: Band 1: 0 - 300 Hz Band 2: 300 - 630 Hz Band 3: 630 - 1080 Hz Band 4: 1080 - 1720 Hz Band 5: 1720 - 2700 Hz Band 6: 2700 - 4400 Hz Band 7: 4400 - 7700 Hz Band 8: 7700 Hz What you'll notice here is that the bands are smaller at lower frequencies - i.e., it's easier for us to tell the difference between 300 and 400 Hz than the difference between 8300 and 8400 Hz. Actually, the bands are wider at the low and high ends, and narrower in the middle. You're comparing them linearly, but frequencies should always be compared logarithmically. The important number is band-top/band-bottom -- ie: how many octaves wide is the band: band 1: infinite (or 15, assuming 20Hz min range) band 2: 2.1 band 3: 1.71 band 4: 1.59 band 5: 1.57 band 6: 1.63 band 7: 1.75 band 8: infinite (or 2.60 assuming 20kHz max range) This makes good sense -- we hear better at the center of our hearing range than we do at either extreme. - Marc ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
Re: [slim] Re: Spectrum Analyzer reversed?
Marc Sherman wrote: Actually, the bands are wider at the low and high ends, and narrower in the middle. You're comparing them linearly, but frequencies should always be compared logarithmically. The important number is band-top/band-bottom -- ie: how many octaves wide is the band: Uh, sorry, the ie isn't quite right there -- the width in octaves is (top/bottom)-1. Just subtract 1 from each of the numbers I gave. - Marc ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
Re: [slim] Re: Spectrum Analyzer reversed?
As long as you're deviating from a Fourier representation of the signal, may I suggest one that's based on perceptual studies? The Bark scale (http://www-ccrma.stanford.edu/~jos/bbt/Bark_Frequency_Scale.html) is based on the idea of critical bands --- namely, people represent the ear as a series of band-pass filters, and the critical band at a given frequency is defined as the width of a rectangular filter that passes the same power as the ear's bandpass filter at that frequency. The key feature here is that the width of this filter varies with frequency. So an 8-band Bark-scale based representation would have bands corresponding to: Band 1: 0 - 300 Hz Band 2: 300 - 630 Hz Band 3: 630 - 1080 Hz Band 4: 1080 - 1720 Hz Band 5: 1720 - 2700 Hz Band 6: 2700 - 4400 Hz Band 7: 4400 - 7700 Hz Band 8: 7700 Hz What you'll notice here is that the bands are smaller at lower frequencies - i.e., it's easier for us to tell the difference between 300 and 400 Hz than the difference between 8300 and 8400 Hz. After taking a quick peek at the code, though, I'm guessing that the FFT for the spectrum analyzer is computed within the Squeezebox 2 itself, so this particular change would have to be implemented in firmware (and maybe not even then, if the FFT is done in hardware). On 7/9/05, Milhouse [EMAIL PROTECTED] wrote: I've generated some test tones (100-3000 in 100Hz increments, then 1000Hz incrememnts up to 14Khz) and it seems that the 8-bar Spectrum Analyzer is not weighting the lower frequencies as strongly as it possibly should. I tested using MP3 format as for some reason my SBG2 wouldn't play the WAV formats. It would appear that the following frequencies correspond to each bar: Code: Bar 1 - 0Hz - 1000Hz Bar 1 2 - 1100Hz - 1900Hz Bar 2 - 2000Hz - 2500Hz Bar 2 3 - 2600Hz - 3000Hz Bar 3 - 4000Hz Bar 4 - 5000Hz Bar 4 5 - 6000Hz Bar 5 6 - 7000Hz Bar 6 - 8000Hz Bar 7 - 9000Hz Bar 7 8 - 10,000Hz Bar 8 - 11,000Hz Bar 7 8 - 12,000Hz Bar 7 - 13,000Hz Bar 6 7 - 14,000Hz Bar 8 14,000 13,000 12,000 11,000 40005000 60007000 80009000 10,000 2600-3000 2000-2500 1100-1900 0 - 1000 Bar 1 | Bar 2 | Bar 3 | Bar 4 | Bar 5 | Bar 6 | Bar 7 | Bar 8 | For some reason frequencies above 11K are begin to appear in lower bars of the analyzer. It would better, I think, if the first 4 bars were used to represent frquencies between 0-3500Hz, with the remaining 4 bars used for frequencies above 3000Hz. This may give a better representation that at present. eg. Code: 11,000+ 10,000 9000 8000 7000 6000 5000 4000 3100-3500 2600-3000 2100-2500 1600-2000 1100-1500 600-1000 0 - 500 Bar 1 | Bar 2 | Bar 3 | Bar 4 | Bar 5 | Bar 6 | Bar 7 | Bar 8 | I'll take a look and see if I can tweak anything in squeezebox2.pm, but as I know next to nothing about Perl I'm not expecting much success! :) -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
Re: [slim] Re: Spectrum Analyzer reversed?
A.J. Aranyosi wrote: snip After taking a quick peek at the code, though, I'm guessing that the FFT for the spectrum analyzer is computed within the Squeezebox 2 itself, so this particular change would have to be implemented in firmware (and maybe not even then, if the FFT is done in hardware). The specturm analyzer and FFT are computed in firmware. The FFT library used is Kiss FFT (http://sourceforge.net/projects/kissfft/). While the firmware is not open-sourced, a close facsimile of the spectrum analyzer generation can be found within Richard Titmuss' excellent Softsqueeze (see http://svn.slimdevices.com/trunk/softsqueeze/src/com/slim/softsqueeze/visualizer/VisualizerSpectrumAnalyser.java?rev=3039view=markup). Any submissions to improve the spectrum analyzer within Softsqueeze could potentially be ported back to the SB2...keeping in mind that the code will need to run in a fixed-point, memory-constrained embedded environment. --Vidur ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
vidurapparao Wrote: The specturm analyzer and FFT are computed in firmware. This was the conclusion I eventually came to but hadn't updated this post - it seems the most one can do by modifying the SlimServer code is adjust the frequency bias. vidurapparao Wrote: The FFT library used is Kiss FFT (http://sourceforge.net/projects/kissfft/). While the firmware is not open-sourced, a close facsimile of the spectrum analyzer generation can be found within Richard Titmuss' xcellent Softsqueeze (see http://tinyurl.com/do8p6. SoftSqueeze does indeed achieve a fairly (but not 100%) accurate representation of an SB2 spectrum analyzer. :) vidurapparao Wrote: Any submissions to improve the spectrum analyzer within Softsqueeze could potentially be ported back to the SB2...keeping in mind that the code will need to run in a fixed-point, memory-constrained embedded environment. --Vidur Sounds tricky, and I think out of my league :( -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
I've generated some test tones (100-3000 in 100Hz increments, then 1000Hz incrememnts up to 14Khz) and it seems that the 8-bar Spectrum Analyzer is not weighting the lower frequencies as strongly as it possibly should. I tested using MP3 format as for some reason my SBG2 wouldn't play the WAV formats. It would appear that the following frequencies correspond to each bar: Code: Bar 1 - 0Hz - 1000Hz Bar 1 2 - 1100Hz - 1900Hz Bar 2 - 2000Hz - 2500Hz Bar 2 3 - 2600Hz - 3000Hz Bar 3 - 4000Hz Bar 4 - 5000Hz Bar 4 5 - 6000Hz Bar 5 6 - 7000Hz Bar 6 - 8000Hz Bar 7 - 9000Hz Bar 7 8 - 10,000Hz Bar 8 - 11,000Hz Bar 7 8 - 12,000Hz Bar 7 - 13,000Hz Bar 6 7 - 14,000Hz Bar 8 14,000 13,000 12,000 11,000 40005000 60007000 80009000 10,000 2600-3000 2000-2500 1100-1900 0 - 1000 Bar 1 | Bar 2 | Bar 3 | Bar 4 | Bar 5 | Bar 6 | Bar 7 | Bar 8 | For some reason frequencies above 11K are begin to appear in lower bars of the analyzer. It would better, I think, if the first 4 bars were used to represent frquencies between 0-3500Hz, with the remaining 4 bars used for frequencies above 3000Hz. This may give a better representation that at present. eg. Code: 11,000+ 10,000 9000 8000 7000 6000 5000 4000 3100-3500 2600-3000 2100-2500 1600-2000 1100-1500 600-1000 0 - 500 Bar 1 | Bar 2 | Bar 3 | Bar 4 | Bar 5 | Bar 6 | Bar 7 | Bar 8 | I'll take a look and see if I can tweak anything in squeezebox2.pm, but as I know next to nothing about Perl I'm not expecting much success! :) -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
I really liked the look of the analogue VU in the gallery on this page - http://www.slimdevices.com/images/gallery/6.jpg ,but the current analogue VU does not look like this. The arrowheads on the needles just look a little naf for my liking. -- oreillymj ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
radish Wrote: Apologies for the poor ascii art but you get the idea. Vidur posted how to adjust the sensitivity a while ago, I may try turning the first band down. A picture is worth a thousand words - never more true in this case, your picture is an accurate representation of the over sensitivity of the left-most band, which distorts the analysis. I'll work on some test tones later in the week and come up with data identifying which tones fall into which band... -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
Use the analog vu instead - it's by far the best screensaver. :-) Max Milhouse Wrote: A picture is worth a thousand words - never more true in this case, your picture is an accurate representation of the over sensitivity of the left-most band, which distorts the analysis. I'll work on some test tones later in the week and come up with data identifying which tones fall into which band... -- max.spicer The wild things roared their terrible roars and gnashed their terrible teeth and rolled their terrible eyes and showed their terrible claws but Max stepped into his private boat and waved good-bye ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
Not sure, I'm referring to the frequency spectrum analyzer, the one with multiple bands for each frequency - it seems high frequencies are on the left, low frequencies on the right which seems to be the opposite of the norm... are you referring to the two-band analyzer which I guess represents left/right channel, although I don't use it so can't be sure :) -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
Re: [slim] Re: Spectrum Analyzer reversed?
Quoting Milhouse [EMAIL PROTECTED]: Not sure, I'm referring to the frequency spectrum analyzer, the one with multiple bands for each frequency - it seems high frequencies are on the left, low frequencies on the right which seems to be the opposite of the norm... are you referring to the two-band analyzer which I guess represents left/right channel, although I don't use it so can't be sure :) The fullscreen spectrum analyser is mirrored, just as max said. The middle is high frequency with the low bands at the left and right extremes. -kdf ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
Actually, I've dug up the thread containing the more detailed explanation of the spectrum analyser from Vidur. http://forums.slimdevices.com/showthread.php?t=13515 -- kdf ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
Thanks for the info kdf, and Max - sorry for my confusion. I tend to use the small spectrum analyzer and remaining time setting which results in 8 bands, each of which (I assumed) represented distinct frequencies... it wasn't obvious there was any mirroring going on as I quite often observe a peak in a left-most band when for example, a cymbal is playing, and bass seems to affect the right most bands. Will now read the links to Vidurs explanation. :) -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
Milhouse Wrote: I tend to use the small spectrum analyzer and remaining time setting which results in 8 bands, each of which (I assumed) represented distinct frequencies... 8-band analyzer: This represents left and right channels summed together, ie mono. The left side of the display is bass and right side is treble. If it doesn't look correct, try a different track having more distinct transients on the high end. Full-screen analyzer: 32 for left ch and 32 for right ch. Left bass is on the left Right bass is on the right To the immediate left and right of the middle of the screen are the left and right treble bands, respectively. -- seanadams ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
[slim] Re: Spectrum Analyzer reversed?
seanadams Wrote: 8-band analyzer: This represents left and right channels summed together, ie mono. The left side of the display is bass and right side is treble. If it doesn't look correct, try a different track having more distinct transients on the high end. I'll do some more investigation and try to find some test tones, shame I can't rip my Avia DVD AV setup disc - I'll try it later in the week if I get the right software... :) Perhaps the limited number of bands is confusing my ear/eye co-ordination, as the left-most band seems to see more activity than would appear reasonable. (Note that this isn't a specific issue with the latest 14 firmware or 6.1b1, it's always been this way.) seanadams Wrote: Full-screen analyzer: 32 for left ch and 32 for right ch. Left bass is on the left Right bass is on the right To the immediate left and right of the middle of the screen are the left and right treble bands, respectively. Right gotcha, that makes sense. The penny has dropped at last! ;) -- Milhouse ___ Discuss mailing list Discuss@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/discuss
