Page 1 of 14 1234511 ... LastLast
Results 1 to 10 of 132

Thread: Grekim and Ethan test dither, jitter, A/D

  1. #1
    Join Date
    Feb 2005
    Location
    New Milford, CT, USA
    Posts
    1,185

    Icon3 Grekim and Ethan test dither, jitter, A/D

    Folks,

    Out forum friend Grekim came to my studio yesterday and we spent a fun four hours playing with our toys. Grekim is a fine musician, and you'll hear his guitar playing in the example files linked below. We did three tests in all:

    * Comparing dithered versus truncated 16-bit files at loud and soft playback levels

    * Listening for jitter by comparing my Delta 66 sound card with its own clock versus clocked by Grekim's Apogee 8000

    * Listening to instruments recorded simultaneously through my SoundBlaster X-Fi card and his Apogee

    DITHER

    For the dither test I loaded into Sound Forge a 24-bit mix Grekim has been working on. I created two 16 bit files from that, one dithered and one truncated. I then played the two 16-bit versions alternately while Grekim listened on my large JBL 4430 loudspeakers at a normal volume level. Since I had two files open at once it was easy to play them in rapid succession with no delay. I played a few seconds of one file, then the same few seconds of the other, then the first again, and so forth repeatedly.

    We played several different short sections of Grekim's tune this way, and neither of us heard any difference between truncated and dithered. Just for fun I found a spot where the ending chord had almost completely faded out, raised the playback volume about 20 to 30 dB, and again played the same section in both files. Even with the volume cranked on a very soft passage we still heard no difference. Even I was a little surprised by that!

    JITTER

    One of the claimed features of using an outboard word clock is improved sound quality due to lower jitter. So to test this we played the same sections in Grekim's mix through my Delta 66 sound card using either its internal clock or the clock in his Apogee 8000. We also tried my SB Live sound card using its internal clock. With this test there was no way to switch instantly because I had to stop playback and change Sound Forge's playback device, and Grekim also had to switch the Apogee. The fastest we managed was about five seconds, and Grekim and I both agreed it was tough to tell if anything really changed. Not that I expected or heard any change myself.

    At one point Grekim thought he heard a change in the stereo image. That part of the tune sounded to me to have a stereo widener effect on one of the instruments, and I heard the same "out of phase" type sound with all three outputs. After going back and forth a few more times Grekim conceded he was not able to identify with certainty any difference between the three output devices.

    SOUNDBLASTER VERSUS APOGEE

    For this test we recorded three different instruments, one after the other, simultaneously through my $25 SoundBlaster and Grekim's $6,000 Apogee 8000. Sonar allows recording from multiple sound cards at once, so I used a splitter to send the output of my Mackie 1202 mixer's preamp to the SoundBlaster's line input and also to the Apogee's line input.

    I didn't want to apply any volume changes or other processing after the fact, so I played a 700 Hz test tone through my loudspeakers to match the record levels as closely as possible by eye using Sonar's record meters. I believe we matched the levels to within at least 1 dB, and audibly both tracks sounded the same volume. I recorded Grekim playing my Yamaha acoustic guitar and a single triangle hit using my DPA 4090 microphone. We also recorded a few clave hits which I played.

    A triangle is very demanding of A/D conversion because it contains frequencies well past 20 KHz, and also contains many different high frequencies. Unlike string and wind instruments, triangles (and cymbals and bells) contain many overtones that are not necessarily related to the fundamental and can also occur closer in frequency. Using Sound Forge's spectrum analyzer I confirmed that the triangle we recorded had substantial energy at 16 different frequencies between 10 KHz and 21.1 KHz. The highest three overtones were at 20,055 Hz, 20,535, and 21,095 Hz. Therefore, this is a demanding test because the A/D converter's filter needs to avoid audible aliasing and IM products caused by those nearby high frequencies.

    Sonar's linked Solo feature makes it very easy to switch playback between the SoundBlaster and Apogee recordings. I enabled Solo on only one track, then linked the Solo buttons on both tracks. So clicking either Solo button toggled playback between one track and the other instantly with no gap. Grekim listened with his expensive headphones, and was unable to hear any difference on any of the three instruments.

    CONCLUSION

    Some people may not like what we found, but that's not my fault. Neither of us heard any difference between dithered and truncated even with very soft material played back at an unnaturally high volume. Nor did we hear any difference between the jitter in my SoundBlaster card, my Delta 66, or Grekim's Apogee. Nor did we hear any difference in the three instruments recorded through my SoundBlaster and his Apogee.

    One failing of this test is we had a bit of low-level hum because my Mackie mixer's preamp direct output is unbalanced. The hum is well below the signal and not audible at normal levels on my SoundBlaster, but it's slightly audible on the tracks we recorded through the Apogee.

    I didn't hide the file names to make a blind test, so here they are and you can listen for yourselves to draw your own conclusions:

    Guitar into SoundBlaster
    Guitar into Apogee
    Claves into SoundBlaster
    Claves into Apogee
    Triangle into SoundBlaster
    Triangle into Apogee

    Note that the above files are all mono, 24 bits, at 44.1 KHz.

    Here's a final thought about critical listening comparisons: It's not so much that we need to do tests like this blind, but switching quickly is key to knowing if the sound really changed. That is, as long as people are being intellectually honest, there's no need to hide from them what they're hearing. However, the A and B versions must be presented in a way that makes it easy to hear if there really is a difference. It seems to me the key to this, besides carefully matching volume levels, is being able to switch instantly back and forth in mid-stream without clicks or drop-outs. Sonar's linked Solo buttons makes this very easy, and I've used that many times to audition stuff like this in the past. It's only a little more difficult to switch quickly in Sound Forge. You load both files and put the cursor in the same place for each. Then clicking either file's Play button stops the other one and starts the current one. Each time you click Play the selected file begins at the same place.

    --Ethan

  2. #2
    Join Date
    Aug 2001
    Location
    Fort Wayne, IN, USA
    Posts
    27,246

    Default

    Re: Dither

    When Scott Massey of MasseyPlugins was here in Nashville last week, he did a whole presentation for the AES members called "Dither-Why Bother?"

    A pretty ballsy move considering some of the names, credits and critical ears that were in the room. I remember him asking "Have you ever heard someone say 'Wow, it's a great record, but they sure messed up on the dither'?" That one got a laugh.

    The other point that he made was "If it's so critical about when and how to dither, how come no one can figure it out for themselves? People are always asking questions about it. If there's a big sonic difference between doing it right and doing it wrong, then how come people (engineers) can't even tell whether they're doing it right or wrong?"

    Some people in the audience thought he was just joking. But after his 15 minute presentation, it was pretty clear he was not. He also pointed to the fact that for some reason in the TDM implementation of his plugins, if you insert one BEFORE the POW-r dither on a channel, the POW-r dither will NOT work. He admitted he was not sure why, but also admitted that it had been that way from the beginning and asked if we could guess how many users had noticed it not working, i.e. how many complaints he had received about from people who discovered it. Not one.
    Lynn Fuston
    3D Audio

    Making beautiful music SEEM easy since 1979.

  3. #3
    runamuck is offline Gold Club Member (1000+ posts)
    Join Date
    Oct 2005
    Location
    Ojai, California
    Posts
    1,518

    Default

    Ethan,

    In your opinion then, the Delta compared to the Apogee yields just as high quailty a mix, even when one is dealing with multiple tracks?

    That is one argument I've read: the quality difference can't be determined by comparing 1 track to another; it's when tracks are stacked up that the difference becomes appreciable.

    I don't know the truth of this never having had the opportunity to test the claims.
    Jim McCarthy

    “Be kind, for everyone you meet is fighting a great battle” -- Philo of Alexandria

  4. #4
    Join Date
    Oct 2003
    Posts
    2,756

    Default

    Ethan, when I get a chance, hopefully this weekend, I'll give the files a listen here. Just for the record, the headphone listening I did was through the Mackie 1202 with Beyerdynamic DT 990's. I may hear more through the Apogee's headphone jack, not sure why I didn't do it at the time.

    Also, Ethan's room is of course top notch. The guitar was a solid top Yamaha, but the strings were turn of the century, vintage

    Finally, thanks Ethan so much for being so gracious and inviting me to your home and taking time for this.
    Last edited by grekim; 01-19-2008 at 08:26 PM.

  5. #5
    Join Date
    Jul 2006
    Posts
    264

    Default

    there go's ethan... our very own amazing randy... always with the debunk...

  6. #6
    Join Date
    Apr 2003
    Location
    Walnut Creek, CA
    Posts
    98

    Default

    There's a buzz in the Apogee Triangle. I don't hear it in any of the other clips.

    Fran

  7. #7
    Join Date
    Feb 2005
    Location
    New Milford, CT, USA
    Posts
    1,185

    Icon3

    Quote Originally Posted by 3daudioinc View Post
    Scott Massey ... The other point that he made was "If it's so critical about when and how to dither, how come no one can figure it out for themselves?
    Yeah, no kidding. Half the time when newbies post questions about stuff like this I suggest they try it themselves and draw their own conclusions, rather than accepting blindly the opinions of anonymous people in a web forum.

    Quote Originally Posted by runamuck View Post
    In your opinion then, the Delta compared to the Apogee yields just as high quailty a mix, even when one is dealing with multiple tracks?
    Sure, why not? A mix is rendered in the DAW program and presented as a single stream to the sound card's D/A converter. I see no difference going in to a sound card either. If two sound cards sound identical when recording one track, it makes no sense to me that some "magic property" from a boutique device will change how the sounds mix together later.

    That is one argument I've read: the quality difference can't be determined by comparing 1 track to another; it's when tracks are stacked up that the difference becomes appreciable.
    People argue all kinds of stuff, especially if it bolsters their belief system and especially if it makes testing their beliefs more difficult. In this case it's nearly impossible to test because nobody can sing or play a musical instrument identically twice in a row. I suppose one could set up a test like Grekim and I did, but with all 20+ microphone preamps sent through splitters to be recorded simultaneously into two different recorders at once. But who's going to do all that? More to the point, it makes no sense to me that something might sound good in isolation but not when combined.

    Quote Originally Posted by grekim View Post
    the strings were turn of the century, vintage
    LOL, I freely admit it. I was going to change the strings last year when I recorded all the guitar parts for my Tele-Vision video. I had just read a tips article by Craig Anderton in EQ magazine where he admonished people for not recording with fresh strings. So just to be ornery I purposely did not change the strings on my Telecaster, or my Yamaha acoustic, or the Strat I borrowed from a friend.

    Quote Originally Posted by dementedchord View Post
    there go's ethan... our very own amazing randy... always with the debunk...
    Hey, it's my job!

    Thanks guys, and I'll be interested to read if others hear can honestly say they hear a difference in the files Grekim and I recorded.

    --Ethan

  8. #8
    Join Date
    Feb 2005
    Location
    New Milford, CT, USA
    Posts
    1,185

    Icon3

    Quote Originally Posted by Fran Guidry View Post
    There's a buzz in the Apogee Triangle. I don't hear it in any of the other clips.
    Do you mean a 60 Hz buzz, or a buzzy quality to the sound? There is some hum in the stuff I recorded through the Apogee, as mentioned in my first post above.

    --Ethan

  9. #9
    Join Date
    Apr 2003
    Location
    Walnut Creek, CA
    Posts
    98

    Default

    Sorry, my bad. 60hz hum, exactly as your initial post indicates.

    As far as hearing differences on my Dynaudio BM6s, I could find none.

    As always, thanks for your posts.

    Fran

  10. #10
    Join Date
    Oct 2003
    Posts
    2,756

    Default

    Quote Originally Posted by Ethan Winer View Post
    Do you mean a 60 Hz buzz, or a buzzy quality to the sound? There is some hum in the stuff I recorded through the Apogee, as mentioned in my first post above.

    --Ethan
    The hum thing is a little disturbing. The SB was looking for a -10 dBu level (I assume) and the Apogee was looking for a +4 dBu level. We cranked the Apogee input "trim" all the way up to make the signal even with the SB input. In retrospect, I should have adjusted a dip switch for -10 nominal level operation which would have required less cranking up the gain. Other explanations could be the path between 1202 and Apogee. I know I've never made a balanced recording with it and had any audible hum.

    By the way, hum or no hum, I don't feel this really hurts any validity of what we did. I don't think 60 cycles and its harmonics will affect at all the way something like a triangle will be recorded. And I doubt there was any significant impact on the guitar track either. Of course we traded off running balanced for doing a split to get two simultaneous recordings, a fact that is very important to the whole experiment.
    Last edited by grekim; 01-19-2008 at 10:07 PM.

Page 1 of 14 1234511 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •