SB3 volume control with 20-bit external DAC

[jonhdahl]

I have a Entech 203.2 external DAC that I would like to use with my SB3. I also want to use the digital volume control on my SB3. Now I understand that the "safe" range with the digital volume control is about 40-100, because the Squeezebox uses 8 bits for volume information (from 24 bits).

But what happens when I send the signal to a 20-bit DAC? Will I lose any info from my music if I drop the volume down to 40? Is (say) 70-100 a safer range? Or does a 20-bit external DAC not affect things at all?

Apologies if this is a dumb question.

[Triggaaar]

You will be fine, the fact that the external DAC is 20 bit does not matter. The squeezebox does not use 8 bits for volume information, but it does start with 24 bits, which is 8 more than were on the CD you probably started with. You will lose bits when reducing the volume digitally, and some cleaver chap has worked out that you can digitally reduce the volume to 40 before reducing your signal below 16 bits. The fact that your external DAC is 20 bit, and the internal DAC is 24 bit, does not negatively change the principle.

[seanadams]

You _ALWAYS_ lose SNR and dynamic range. The "you still have all the bits" concept is completely flawed.

You MUST match your source to your amp using analog attenuation. You can use 1) the gain controls on your amp 2) a preamp or 3) a RCA in-line attenuator or 4) Transporter's built-in jumpers.

Use the digital volume for day-to-day adjustment within your normal listening range, not to compensate for a badly matched system.

This has been discussed many times here, but I won't refer you to our archives as there have been far too many people still getting it wrong. Instead, here's a detailed and correct explanation from Lavry (login needed):

http://lavryengineering.com/lavry_fo...topic.php&t=76

If you don't "believe" the theory (which many people don't for some reason) here is a simple test which one customer did which gives the expected results. Note that he is using older software which shows the volume range as 0-40. In the current software it is 0-100.

http://mysite.verizon.net/forumwebsp...rts/Volume.htm

[seanadams]

You will be fine, the fact that the external DAC is 20 bit does not matter. The squeezebox does not use 8 bits for volume information, but it does start with 24 bits, which is 8 more than were on the CD you probably started with. You will lose bits when reducing the volume digitally, and some cleaver chap has worked out that you can digitally reduce the volume to 40 before reducing your signal below 16 bits. The fact that your external DAC is 20 bit, and the internal DAC is 24 bit, does not negatively change the principle.

This is completely, 100% wrong. It doesn't matter how many people say this, it is still wrong.

[Triggaaar]

Hi Sean. Is the info in that first link too vast to cut & paste here (to save everyone interested in this topic registering)?

Where I use squeezeboxes, I have my maximum volume set by pre/integrated amps, and I then use the squeezeboxes to adjust the volume down, and while I expected a reduced SNR, I thought this would be insignificant, as I was reducing the volume at the same time (maybe it's still significant, but I've never noticed it). I can see this would not be the same if you were already lowering the volume on the squeezebox to get to your maximum volume setting, where the reduced SNR would be more noticeable (eg, with the Entech DAC & no preamp).

I assume the details of losing dynamic range by digitally reducing the volume is in the link you posted, so I shall go study.

[wshields]

So if you send digital output to a dac I assume that you should use fixed digital out of either a SB or Transporter and then adjust volume after entering analog domain, right?

How about when using analog out of Trasporter to a preamp? Does using volume control on a preamp act differently than volume control on the transporter? Any general suggestions on where to adjust volume or how to figure the correct ranges on each piece of gear?

The link to the Lavry site doesn't seem to work right. I get sent to their general forum start and not to any specific topic.

I would like to suggest you should write a FAQ about this whole volume setting as there does seem to be so much conflicting information given.

Thanks

[mr_bill]

You _ALWAYS_ lose SNR and dynamic range. The "you still have all the bits" concept is completely flawed.

You MUST match your source to your amp using analog attenuation. You can use 1) the gain controls on your amp 2) a preamp or 3) a RCA in-line attenuator or 4) Transporter's built-in jumpers.

Use the digital volume for day-to-day adjustment within your normal listening range, not to compensate for a badly matched system.

This has been discussed many times here, but I won't refer you to our archives as there have been far too many people still getting it wrong. Instead, here's a detailed and correct explanation from Lavry (login needed):

http://lavryengineering.com/lavry_fo...topic.php&t=76

If you don't "believe" the theory (which many people don't for some reason) here is a simple test which one customer did which gives the expected results. Note that he is using older software which shows the volume range as 0-40. In the current software it is 0-100.

http://mysite.verizon.net/forumwebsp...rts/Volume.htm

Sean,

As an example, could you explain to us how to best use the jumpers in the Transporter and the volume range of 0-100 to properly match source to amp. That would be very helpful.

If you have an SB3 and Benchmark Dac1, you can use the Benchmark's internal jumpers to match the source to amp also (I think!!)
Thanks,
Bill

[seanadams]

Sean,

As an example, could you explain to us how to best use the jumpers in the Transporter and the volume range of 0-100 to properly match source to amp. That would be very helpful.

The new 0 to 100 scale is, I believe, true decibels. (In the past when we used only 40 steps, it was a more complicated curve designed to stretch out the low end of the range). So -10 corresponds to 90, -20 to 80, and -30 to 70.

If you have an SB3 and Benchmark Dac1, you can use the Benchmark's internal jumpers to match the source to amp also (I think!!)
Thanks,
Bill

Correct - exactly the same concept.

[Ben Diss]

That is one tough read. It doesn't help that our friend Dan is a bit of a prickly pear. If the link doesn't work, look for the thread titled "DA10 for the main pair in a 5.1 setup".

-Ben

[mr_bill]

The new 0 to 100 scale is, I believe, true decibels. (In the past when we used only 40 steps, it was a more complicated curve designed to stretch out the low end of the range). So -10 corresponds to 90, -20 to 80, and -30 to 70.



Correct - exactly the same concept.

Sean,
So, if I set up my inernal jumpers on my Benchmark Dac (or Transporter for that matter) so if the SB3 volume reads 70 and my decibel meter in room reads 70 db then am I set up and getting maximum SNR, resolution and performance? Would I still need a preamp performance related to matching or volume?
Thanks and I think I finally understand,
Bill