Thoughts on dithering.....

[elwoodblues1969]

For a long while now,I have been tormented by the decimation of audio quality when converting WAV to MP3 & regardless of all of the upgrades in gear & painstaking attention to detail in my mixing,I am still left with that horrible warble sound!
At first I thought the problem was with the FreeRip program I had used(uploading from a CD from my old recorder which was 16 bit)....so then I learned to transfer my music directly from my old Zoom 8HD recorder in WAV format directly to my PC,but no improvement.
So I took another step up & utilized the Audacity program,along with upgrading to the 24 bit Tascam 2488neo multitracker.....but no improvment...just can't shake that terrible warbling sound.
Now I am at a point where I have learned to get the most of my Korg keyboards,by fully utilizing all of their sound mastering potential and also brightening & adding more depth to my recordings by upgrading from my Tascam's built in effects,to the Lexicon processor(which improved the stereo field greatly,but did not eliminate that warbling sound that's exclusively inherent in MP3 recordings.
At this point in time,I suspect that the dither switch in the Tascam is to blame,so perhaps I should just transfer my Tascam recordings to my PC without dithering and then do the dithering in Audacity?

Any advice on this matter would be greatly appreciated!

Thanks,

-Thom

[folderol]

I remember Oren had this problem with one of out collaborations. I can't remeber what the final answer was. However I would suggest that conversion to mp3 should always be done in the very last piece of kit the music sees - in your case, Audacity. What bit rate are you using? My experience is that variable bit rate (VBR)  gives the best results. I doubt there are any players these days that can't do VBR, but there are still lots of commercial programs that can't generate it!

I also doubt it's a dither problem. I've attached a copy of a very interesting article I found on dithering.

Hope this helps.

[elwoodblues1969]

Will,

Thanks very much for the article,as it's quite fascinating.In relation to my issue,I think the cause of the warbling sound may be a result of me putting my music through the dithering process twice?Meaning that if I don't dither it in the Tascam & leave the dithering job to Audacity,then maybe I'll nail down the solution.
I've also decided to change the kbps rate to 256,instead of 128,so I'll see what happens next time I run a song through my Tascam.

-Thom

[Wyatt]

I've also decided to change the kbps rate to 256,instead of 128,so I'll see what happens next time I run a song through my Tascam.[/b]

-Thom

I don't know if this will have bearing on your problem, but twice I had deal-killer problems with mp3 conversions.

I had two trombones playing a duet, and three quarters of the way through the song it got really ragged..even after several attempts at conversion. The .wav file was perfectly fine.

Increasing from 128 kbs to 160 kbs solved the problem on one, and I had to go up to 192 on the second one.

[elwoodblues1969]

Yeah....it's funny how the MP3 conversion only effects certain sounds and/or songs........for me,the conversion usually targets my bass & string tracks.
Perhaps changing the kbps rate won't change much of anything....but any improvement at all is worth a go at it.
Thanks for your input Wyatt.

-Thom

[Wyatt]

Yeah....it's funny how the MP3 conversion only effects certain sounds and/or songs........for me,the conversion usually targets my bass & string tracks.
Perhaps changing the kbps rate won't change much of anything....but any improvement at all is worth a go at it.
Thanks for your input Wyatt.

-Thom

If changing to 256 kbs doesn't solve the problem, then it must be something else.

[Alienz]

With VBR I find the hihats, cymbals etc get so warbled, I never use it
And since I got a new hifi -amp and speakers I dont listen to 128k files anymore, the difference with 256 and up is just mindboggling to me, never heard that difference before on my old system

[Oren]

Thom,

First of all, dither is something I never do. Dithering is a term some people use interchangeably with sample-rate conversion, but dithering is actually a method of introducing noise into a signal to hide the results of a sloppy conversion. So avoid dithering - turn it off. Plan your work so that sample-rate conversions are kept to a minimum.

Secondly, do your "lossy" compression as the last step, and don't be tempted to expand back to wave format for further processing, nor waste time processing the .mp3 or .ogg file.

Constant bit-rate .mp3 performance in Lame has been upgraded recently, so using their variable bit-rate method is no longer necessary (although the VBR performance is still superior). Ogg Vorbis is, by definition, a variable bit-rate compression codec, and it is my choice of "lossy" formats.

[Wyatt]

First of all, dither is something I never do. Dithering is a term some people use interchangeably with sample-rate conversion, but dithering is actually a method of introducing noise into a signal to hide the results of a sloppy conversion. So avoid dithering - turn it off. Plan your work so that sample-rate conversions are kept to a minimum.

You got me to thinking again, amigo..   

Currently, when I work in Reason it is @ 24/96, and since Audition does not work with 24 bit, but only 16 bit or 32 bit float, I have been exporting audio from Reason @ 16/44.1, since that is the destination bit depth/sample rate of all my projects.

So  I can disable dither in Reason when I export/downsample..ok..that's easy enough, but would I be better off not downsampling out of Reason in the first place, but just opening the 24 bit files in Audition as 32 bit float, and then downsample to CD quality at the end of the trail?

I have heard that you are best off to maintain the highest level of quality for as long as possible, but I was never impressed with the idea of upsampling.

Thanks in advance!





 

[elwoodblues1969]

Oren,

Okay...lesson well received & applied to good use....just completed the process in accordance with your advice & my MP3 sounds fantastic!!!

Thanks!

-Thom

[rharv]

Doing ANY processing after dithering is a no-no
It'll very often come back to haunt you.

It CAN be a beneficial process when done correctly and with a decent dithering app.
That said, poor dithering is worse than no dithering IMO.

Just like trying to go back and reprocess an MP3, trying to reprocess a dithered piece of audio will often inject problems.

It's really only necessary when going from 24 bit to 16 bit for final CD.

Most Dither apps will tell you (quite fervently) not to dither until the final step.

A lot of people read that dithering adds noise and immediately think 'bad idea'.
The problem is that truncating 24bit depth down to 16 without dithering can be 'sharp'.

The process softens the edges as it were.

[Wyatt]

Doing ANY processing after dithering is a no-no
It'll very often come back to haunt you.

It CAN be a beneficial process when done correctly and with a decent dithering app.

Just like trying to go back and reprocess an MP3, trying to reprocess a dithered piece of audio will often inject problems.

It's really only necessary when going from 24 bit to 16 bit for final CD.

Most Dither apps will tell you (quite fervently) not to dither until the final step.

Thanks a lot..I appreciate your advice.

[folderol]

A point worth keeping in mind is that not all MP3 encoders are born equal

Indeed, LAME stands for L(ame) Aint Mp3 Encoder. Although it produces files that are playable by any MP3 player, they are actually generated with different (patent and license free) code.

Most MP3 encoders ceased development years ago so will never improve.

[rharv]

If interested in more, here is another article on it -
http://www.izotope.com/products/audio/ozone/OzoneDitheringGuide.pdf

I personally like the dithering in Ozone above some others I own, but  I speak only thru trial and listening; no testing done..

[Wyatt]

If interested in more, here is another article on it -
http://www.izotope.com/products/audio/ozone/OzoneDitheringGuide.pdf

I personally like the dithering in Ozone above some others I own, but  I speak only thru trial and listening; no testing done..

Didn't know about this article; I'll definitely check it out.

I've been very impressed with what I have heard from folks who use Ozone 4, and the Izotope multiband compressor in Audition 3 is very nice..quality stuff.