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JEFF - TASCAM GUY - 24 to 16-bit dithering?


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jeff (or anybody who might know this) - i am recording at 24-bit on a roland VS1880 (MTP mode), and i do mix downs via spdif (coax) to an external tascam CD-RW700, which of course is 16-bit. does the tascam unit automatically dither the 24-bit input to 16-bit? or does it truncate the 24-bit signal? should i use the roland to dither down before sending the signal out to the tascam?

jnorman

sunridge studios

salem, oregon

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J, Unless I'm mistaken, the CD-RW700 only does 16bit, no dither. Thereofre if it is fed a 24 bit signal, it will truncuate. It does sample rate conversion....32kHz~48kHz to 44.1kHz. I have one of these units, butI use it almost exclusively to record from the analog ins... take a look at the manual... (click on the link for the pdf file) http://www.tascam.com/products/cd_recorders/cdrw700/index.php hope this helps NYC Drew
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I responded to the original question in an email, but NYC Drew is right: the settings to dither versus truncate the original signal would be something set at the VS-1880. If the 24-bit signal gets to the CD-RW700 unchanged, it will indeed be truncated. CDs only function at 16-bit/44.1kHz. And yes, dither at the source if you can, as long as their dithering algorithm doesn't sound like crap. Just listen first...that's all. I'm sure it's fine. - Jeff
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jeff - thanks, and i got your email about this. i am confused - the specs on the 700 indicate that it has 24-bit ADA converters. so if i input an analog signal, it will convert it to 24-bit and then immediately truncate it to 16-bit to burn it on the CD? why not just put 16-bit converters in there to begin with? if it reduces quality to truncate the internal 24-bit signal, why doesnt the 700 have the ability to dither, or is the quality loss due to this truncation not that noticeable? is the sound of 24-bit truncated to 16-bit different than if it had been recorded originally in 16-bit?

jnorman

sunridge studios

salem, oregon

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jnorman...yes, it has 24-bit A/D and D/A converters. Your first post indicated you were using the S/PDIF inputs. Obviously, converters are on the analog inputs and outputs...they convert the analog signals to digital and back again. Using converters that are higher than 16-bit allows you to maximize the sonic capabilities of the input signal. I don't want to get into the rocket-science part of this explanation (Craig can definitely explain it better than me), but yes, the end result is that it sounds better. In any case, don't use the analog inputs for this reason. The less times you can avoid having your signal converted from one format to the next, the better the chances of having less degradation. Go ahead and use the S/PDIF inputs and let the CD player truncate the bits, or see if your Roland can be set to dither in a way you find aesthetically pleasing. - Jeff
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jeff - because of my continued confusion on this issue, i spoke with jeff hoffman in tascam's technical support group, and he indicates that the CD-RW700 does indeed dither the 24-bit signal to 16-bit - it does not truncate the signal. the dithering capability is built-in to the DSP processor. could you please follow up on this with your tech engineers and see if we can get a definitive answer? BTW, regardless of the outcome of this, the CD-RW700 is a fabulous piece of equipment, and one of the best buys i have made for my studio. thanks.

jnorman

sunridge studios

salem, oregon

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to further confuse it, i got an email from tech support in england that says the CD-RW700 truncates the signal. i guess i just dont understand why tascam would design a unit with 24-bit converters in it, and a comprehensive DSP processor, and then use truncation internally before burning the CD - if you have DSP available on-board, why not design it to dither the signal instead of truncating? this means that any analog signal or 24-bit signal brought into the unit will suffer from truncation at the CD stage. are there other, more professional CD recorders that provide dithering internally following DSP functions?

jnorman

sunridge studios

salem, oregon

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jnorman, I did a little digging, and in fact spoke to the engineer who designed the CD-RW700. Much to my pleasant surprise, it turns out that Jeff Hoffman in tech support was right, and I and the U.K. guys were wrong. In other words, the inputs do indeed dither the signal. The miscommunication on our side involved one guy using the word "cut" (which I interpreted as truncate -- makes sense, huh?) when referring to the bit depth when it got to the CD (of course). I will let the U.K. guys know that in future requests of this nature, the correct answer is dither. That way, we won't be confusing people around the world, which apparently is our specialty right now. :) - Jeff
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jeff - one other little thing - a guy over at the VSPlanet forum asked if i was sure the CD-RW700 could accept 24-bit signals, he thought it would only accept 16-bit. i told him that since the unit has 24-bit ADA converters, it should handle 24-bit input signals via SPDIF and maintain that resolution throughout the DSP processing, and then dither the signal down to 16-bit as the final step. is this correct? second, what does the unit do if you input a 16-bit signal via coax? since the DSP is probably all 24-bit, i would guess the 16-bit signal would be resampled to 24-bit, then run through the DSP, then dithered back to 16 to burn the CD. is this correct?

jnorman

sunridge studios

salem, oregon

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[quote]Originally posted by jnorman: [b]i told him that since the unit has 24-bit ADA converters, it should handle 24-bit input signals via SPDIF and maintain that resolution throughout the DSP processing, and then dither the signal down to 16-bit as the final step. is this correct?[/b][/quote] Not quite. The converters are on the analog inputs and outputs. Dithering is a seperate process, since the signals coming in are already digital and are remaining so, since you're using the S/PDIF input (not the analog input). [quote][b]second, what does the unit do if you input a 16-bit signal via coax?[/b][/quote] It remains a 16-bit signal throughout, right through burning the disc. Here's where you're getting confused. ALL CD burners that use the Red Book standard (the one that you can play in a consumer CD player) use a 16-bit bit depth and a 44.1kHz sampling rate. The more modern professional CD burners (like the CD-RW700) can accept 24-bit signals via the process I've described above. But once it gets inside the burner, it doesn't matter whether it's from the A/D converters on the analog inputs or the S/PDIF input which will then dither the signal: it's 16-bit at that point. Understand? I know these concepts are a bit hard to grasp until you've lived with them for awhile. Then, one day, everything becomes clear and you become a guru of all things with 1's and 0's. :) - Jeff
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Jeff, or anyone else who knows: Hi, I'm "the guy at VSPlanet". I have a few questions which I really hope you can answer, but let me just first reiterate what has been talked about so far. I've read through the entire thread. and thus far, I have picked up on the following: 1.) A 24-bit DIGITAL INPUT signal gets dithered to 16-bits before burning. 2.) An ANALOG INPUT signal is converted (to 24-bits, right?) and dithered to 16-bits for burning. 3.) A 16-bit DIGITAL INPUT signal is NEVER converted to 24-bits, but stays 16-bits to the burner. Ok, now, I have a couple of VERY IMPORTANT questions, questions which literally a legion of CDRW700/2000 users are wanting the answers for. Here they are: 1.) If you set the machine to MONITOR an ANALOG INPUT signal, is the DIGITAL OUTPUTS outputting a purely 24-bit signal (meaning never downconverted to 16-bits)? 2.) If you connect a 24-bit DIGITAL source to the INPUT and set the machine to MONITOR that input, is the ANALOG OUTPUT coming directly from the 24-bit DAC? Or is it first dithered to 16-bits then converted to analog? Question number one is the BIG ONE, although #2 is almost as much so. But #1 is one the whole CDRW700/2000 community is waiting for. One of the moderators back at the Tascam Forum mentioned something to the effect that earth and oceans would have to be traversed and language barriers broken down in order to find the answer to that question. I hope it's not as hard. Thanks.
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  • 2 weeks later...
The mystery gets deeper. The plot thickens. Insert other thriller cliche here... [b]1.) If you set the machine to MONITOR an ANALOG INPUT signal, is the DIGITAL OUTPUTS outputting a purely 24-bit signal (meaning never downconverted to 16-bits)?[/b] We've asked this specifically to the designer of the CD-RW machines in Japan, and haven't received a decipherable specific response. Our product manager's hunch is that the answer is no. But that's all I have right now. [b]2.) If you connect a 24-bit DIGITAL source to the INPUT and set the machine to MONITOR that input, is the ANALOG OUTPUT coming directly from the 24-bit DAC? Or is it first dithered to 16-bits then converted to analog?[/b] Our product manager believes the signal is dithered and sample rate converted right away. However, for some reason, we don't have an official answer on that from Japan either. I think this whole thing is tied into the Kennedy assasinations and the Enron debacle, but I could be wrong. Remember, just because you're paranoid doesn't mean everyone's not out to get you. :eek: - Jeff
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Thanks Jeff! Keep digging for the answers. Of course, we all realize that a "yes" to both questions automatically means that owners of CDRW2000s (and probably 700s) "suddenly" will acquire standalone 24-bit DAC and 24-bit ADC converter boxes. Although your product manager seems to be refuting both cases.
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I'dd [i]really[/i] rather give you the most conservative answer on this than building you up for a possible letdown if this is not the case (which I also suspect). My preference is to underpromise and overdeliver, as opposed to the reverse. No wonder I don't make more money as a marketing weasel! ;) - Jeff
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