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  1. Old Comment
    fas42's Avatar

    A Better Audio Comparison Tool

    I have picked an interesting pair of tracks to use as a test run: very poor quality in the recording sense, one from a CD, the other an extract of fairly high resolution audio from a YouTube video - are they the same track ...??

    No, as mentioned above they run at different speeds, and further, the speed alters during the track - taking the CD as reference, the AAC version changes speed as it plays! The latter appears not to be vinyl, and in fact is quieter in a noise sense than the CD, looking at the waveform, at high frequencies! Even more 'laughable' - the spectrum of the YouTube version shows the intrinsic above 10kHz band is "better", there's more there! To listen to them at a casual level they sound very similar - but visually there is substantial, obvious variance between the waveforms. Which is not to say that the compressed version has "lost" information in an obvious sense - every single wriggle of the CD version is perfectly matched by a wriggle in the YouTube variant, just that the wriggles don't beautifully match, they won't "subtract" neatly.

    Interesting ...
    permalink
    Posted 24th June 2014 at 01:46 AM by fas42 fas42 is offline
  2. Old Comment
    fas42's Avatar

    Tweeter DAC

    Richard, just refresh my memory on how those multiple TDA1387s are working; IOW, what the circuit for the above is, please ...

    Thanks,
    permalink
    Posted 23rd June 2014 at 11:36 PM by fas42 fas42 is offline
  3. Old Comment
    abraxalito's Avatar

    Tweeter DAC

    Thanks Frank! Certainly I'm passionate about getting the very best sound....
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    Posted 23rd June 2014 at 12:52 AM by abraxalito abraxalito is online now
  4. Old Comment
    fas42's Avatar

    Tweeter DAC

    Richard, can't but repeat that your energy and enthusiasm is very impressive ...
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    Posted 23rd June 2014 at 12:01 AM by fas42 fas42 is offline
  5. Old Comment
    fas42's Avatar

    Fix it time for PC monitor speakers

    Duuuhh ... still haven't done the organ piece, life conspires at the moment, unfortunately ...

    Anyway, a big sigh of relief - I had an album from the library, MPD Limited, 60's Oz pop, which was a very bad transfer, or the master was in poor shape. The sound was almost impossible, and I thought I might not be able to recover listenable quality ... so today I pulled out a lot more stops, essentially making the playback electrical environment even more benign than usual - and that did the trick, high 5's!!! The recording has lots of upper midrange, and reverb was used freely in the production; combine that with poor transfer quality, and it's a recipe for an audio headache! Absolutely minimal degradation in the playback chain is essential for such recordings to bear fruit, and I needed more rounds of effort than usual to get the inherent distortion under control ...
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    Posted 22nd June 2014 at 06:23 AM by fas42 fas42 is offline
  6. Old Comment
    permalink
    Posted 21st June 2014 at 01:53 PM by SteB SteB is offline
  7. Old Comment
    fas42's Avatar

    A Better Audio Comparison Tool

    Octave is looking very good - still chuggin' along, feeling my way into the language - which is what it is, Yet Another Tool for playing with numbers. It's demonstrating a very good ability for performing comparison exercises - I've got 2 versions of a music track - which are at different speeds, therefore start and stop times don't nicely mesh - currently working on approaches to get the two to synchronise in meaningful ways ...
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    Posted 19th June 2014 at 01:04 AM by fas42 fas42 is offline
  8. Old Comment

    2013 Holiday Projects - Ridding the system of resistor problems

    Hi wlowes,

    As you know, I am an inexperienced diyer.


    Please allow me to make a copy of a post I insert in another forum.


    I assembled a very nice LM3886 power amp with the help of someone.
    This amp has dual mono psu with some BL gates on it, and LDR resistors in the amp board. Everything is well wired with a nice copper foil from 47 Labs in the output for speakers. For signal I used silver wire, very thin. Nothing new but it works very well.

    I am using this amp with the Essence full range with Jordan drivers, from 47LAbs. They have 87db but they are an easy load to drive. The amp drives them with authority. Once I had an Anedio D2 dac (with vol control), directly connected to the amp. It worked just fine.

    NOW, I'm programming to buy a first generation Metrum Octave and have it upgraded from Paul Hines - essencially 8 better regulators and a totally new psu. This is an easy solution for me, very simple, no diy headache. I'll learn for more complicate projects but meanwhile I can have a decent system working. I want to connect it to the output stage from Lampizator, with the big tube, the best version if possible. If not, I begin with a modest version and upgrade on the board, later. Between dac and lampizator I am thinking about an autoformer from Intact Audio. I am seriously thinking about puting everything in the same box to avoid cables and plugs, but am not sure yet, this is a very radical decision - but reversible anyway.

    I have coper foil speaker cables and interconnects.

    The question is : what are the differences between the autoformer modules 350 us and the autoformer vol control? Does this allready assembled 350 us version have the right values to my project?


    Thank you!

    Amp
    Amp
    Amp
    Shelf
    Full range
    permalink
    Posted 18th June 2014 at 01:32 PM by polaron polaron is offline
  9. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    Yeah you found it. I found that introducing my passive filter after the TDA1387 DAC really gave a kind of 'holographic' feel to the soundstage which I'd not experienced before. I wrote about it on WBF here - Digital that sounds like analog
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    Posted 16th June 2014 at 03:49 AM by abraxalito abraxalito is online now
  10. Old Comment

    Tweeter line level passive XO

    Richard, would this be the material about IMD?
    http://www.davidgriesinger.com/intermod.ppt

    Quoting David Griesinger:
    "The various tweeters tested – 3 metal dome tweeters and one soft dome tweeter – produce insignificant amounts of intermodulation products below 20kHz when driven by ultrasonic signals.
    Amplifier distortion can produce distortion products below 20kHz that are audible (with difficulty) in the absence of other signals below 20kHz.
    But with a high quality amplifier these distortion products are not audible in the presence of even extraordinary ultrasonic sources such as rattling keys.
    Unless the amplifier is driven into clipping."
    permalink
    Posted 16th June 2014 at 03:33 AM by Alexandre Alexandre is offline
  11. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    Yeah the high level of noise is the thing from outer space as regards audio technology.

    I think Thorsten has done some back of the envelope kinds of calculations (maybe on AudioAsylum?) about DSD's resolution. If you bear in mind that its 64X OS but there are only two levels then in one sample interval, how many different analog levels can be created with a succession of 64 0 or 1's? The answer is nothing like 16bit PCM - if you have all 64 as 1's that's the positive extreme, all 64 as 0's that's the negative. In between - well flip one bit from 1 to 0 this gives 63 1s and 1 0. What's the difference in level when averaged out? One part in 64 ISTM, therefore 6bits. Of course going to lower frequencies you get more bits in the averaging so the resolution seems to go up with lower freq, maybe this is why DSD sounds best in the bass?
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    Posted 16th June 2014 at 03:09 AM by abraxalito abraxalito is online now
  12. Old Comment

    Tweeter line level passive XO

    I agree, that is just ridiculous. Whats alien is the high levels of noise, that have to be dealt with in DSD.

    At least he admitted the non-oversampling dac was the sanity check!
    permalink
    Posted 16th June 2014 at 02:23 AM by Alexandre Alexandre is offline
  13. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    Alex - I've been over to that interview with Ed Meitner and I realized I must have read it before because its so obvious Ed's been drinking DSD-flavoured Koolaid. The kinds of excuses he comes up with for why he thinks DSD beats PCM read like post-purchase rationalizations of someone who's spent a lot of money on a new toy and is talking themself up so as not to admit making a mistake. There's just so much religious nonsense - like

    To convert audio into PCM is a very alien thing,

    Imagine what happens at your zero crossing. You have all those bits flipping.


    You have minimal resolution at zero crossing, whereby with DSD you have maximum resolution and on and on.

    So now look at a PCM signal at zero crossing, and all you’ve got at that moment where it crosses zero is you have zero-bit resolution. The only resolution you’ve got is dither.


    Then later on he's claiming DSD is no worse for jitter than PCM is. I just have to laugh
    permalink
    Posted 15th June 2014 at 10:46 AM by abraxalito abraxalito is online now
  14. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    Yeah they look promising - you can use sellotape or paper to make the gap and it doesn't matter about having the gap on the outside as well, it just means you've effectively got twice the thickness of the paper (or sellotape) as your gap. Probably you'll need a gap between 0.2 and 0.5mm to get these to having a useful AL value (the cores I use are AL=250nH).

    Having no bobbins is a bigger drawback than having no gap I fear. You could try using a wooden dowel and wrap some stiff paper around it as a kind of former but then there's no way to constrain the windings at each end.

    Progress update - I wound all the coils and I've finished wiring up one channel. It worked first time - I connected the siggen (fortunately it has 50ohm output impedance) and my AC voltmeter to the other end. At 1kHz, no output but stepping up the frequency to 4kHz, bingo! Another 'works first time' passive filter
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    Posted 15th June 2014 at 12:16 AM by abraxalito abraxalito is online now
  15. Old Comment

    Tweeter line level passive XO

    These are looking good: 20pcs Pot Core P26 16 4600UH 25 5mm x 8mm Ferrite New Military Surplus | eBay
    Too bad the bobbins are not included.
    Do you make the gap on the center of the core only?
    (I could use stacked paper to make a gap, but that would leave a gap on the ouside as well...)
    permalink
    Posted 14th June 2014 at 06:30 PM by Alexandre Alexandre is offline
  16. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    At a guess - almost certainly it'll use a linear phase FIR to upsample, so there will be pre-ringing and post-ringing. But the ringing is almost certainly ultrasonic unless you can hear above 20kHz.

    I think Mouser has some ferrite cores, problem is with those that they weren't gapped ones last time I looked. A bit tricky to get into grinding down ferrite - apparently its possible with the right kind of emery paper but I've never tried that. Or perhaps a diamond nail-file would do the trick?
    permalink
    Posted 14th June 2014 at 09:57 AM by abraxalito abraxalito is online now
  17. Old Comment

    Tweeter line level passive XO

    Hmmm, theres one test Ive got to do now, curiosity arised... My only source is PC and I upsample to 88.2 or 96KHz inside J.River... Now I want to know what sort of filter it employs and wheter or not it adds pre-ringing. Need to run some step functions and look at the output.
    permalink
    Posted 14th June 2014 at 05:31 AM by Alexandre Alexandre is offline
  18. Old Comment
    abraxalito's Avatar

    Tweeter line level passive XO

    Getting the Q right - well actually this is really about aiming for the highest possible Q. When I first started playing with passive filters that was my biggest problem - although low freq Q didn't matter too much (I was building AAFs with cutoffs near 20kHz, the cutoff freq is where Q matters most) I couldn't get the 20kHz Q high enough no matter how hard I tried.

    Then I discovered ferrites with air gaps, and haven't looked back. Getting HF Qs in the region of 200 isn't a big problem now, and rarely do I need such a high value. I've only used multifilar windings (like Litz wire) on my classD amp where I needed low loss at 300kHz. I'm using wire with about 0.44mm diameter for this PLLXO and the LCR meter shows the losses are less than 50% higher at 20kHz than at 1kHz, so this isn't a problem. But going higher in diameter I'll avoid for where I need decent HF Q.
    permalink
    Posted 14th June 2014 at 01:28 AM by abraxalito abraxalito is online now
  19. Old Comment

    Tweeter line level passive XO

    OK, now Im seriously interested in the passive filters

    Theres so much to inductors (core material, air gaps, multi-filar windings, getting the Q right - do you add the resistors to tune Q?)

    The problem is that I would have to wait one month or more if I ordered cores from china... No local sources that are affordable.
    permalink
    Posted 14th June 2014 at 12:41 AM by Alexandre Alexandre is offline
  20. Old Comment

    Tweeter line level passive XO

    Im not familiar with dsd, but I would imagine commercial interests play a role too...
    He also said the "one FS converter" was the sanity check.
    (If anyone reading this is wondering what "one FS" means: its the same as non-oversampling!)
    permalink
    Posted 14th June 2014 at 12:25 AM by Alexandre Alexandre is offline
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