DAC/Amp volume difference, USB input vs coax

[rarewolf]

Considering the following two cases of streaming from my Jriver server to my Topping E70V/L70 stack, DCA Noire cans, high gain…

(1) Via USB from iPhone 15 (volume max), or via USB from iBasso DAP (which recognizes the DAC, i.e., volume max)

(2) Via WiiM coax out, volume setting 100%

My understanding is that for both cases above, the output is digital and that, by definition, both should be identical (… i.e., bitperfect” …?). Both are the result of sending the same file from the server, the only difference being USB versus coax, and the DAC should be receiving the same digital data(?)

However, the volume setting for a comfortable listening level from the amp for case (1) is -20db (approximately 80%), and for case (2) -40db (60%) …!?

There must be something going on with the input to the DAC. I suppose it can be explained if the data in one case is read (interpreted) as an absolute value, and in the other case interpreted relative to a maximum value (i.e., the absolute value inside a larger container). Or my interpretation of how to send “bitperfect” data via USB or coax needs an education…(?)

 

[MaxwellsEq]

Considering the following two cases of streaming from my Jriver server to my Topping E70V/L70 stack, DCA Noire cans, high gain…

(1) Via USB from iPhone 15 (volume max), or via USB from iBasso DAP (which recognizes the DAC, i.e., volume max)

(2) Via WiiM coax out, volume setting 100%

My understanding is that for both cases above, the output is digital and that, by definition, both should be identical (… i.e., bitperfect” …?). Both are the result of sending the same file from the server, the only difference being USB versus coax, and the DAC should be receiving the same digital data(?)

However, the volume setting for a comfortable listening level from the amp for case (1) is -20db (approximately 80%), and for case (2) -40db (60%) …!?

There must be something going on with the input to the DAC. I suppose it can be explained if the data in one case is read (interpreted) as an absolute value, and in the other case interpreted relative to a maximum value (i.e., the absolute value inside a larger container). Or my interpretation of how to send “bitperfect” data via USB or coax needs an education…(?)

Have you confirmed it is bit-perfect from both rather than assumed?

 

[rarewolf]

Have you confirmed it is bit-perfect from both rather than assumed?

The DAC indicates the same sampling rate, in this case 96kHz, but sampling rate has nothing to do with volume. I can only assume both are bitperfect because of the general rule, “if you want bitperfect set the source volume to 100% and no EQ”

I suppose I can assume with greater confidence the DAP is delivering bitperfect because there is no way to control volume at the source. The iPhone is at the same volume only if set at 100%.

SPDIF coax should provide the same bitperfect confidence. As i understand, SPDIF delivers bitperfect by design, and the WiiM’s output setting for volume is also 100% (… as if it would have any effect). The mystery is that the WiiM’s coax output is physically much louder (… SPDIF optical same result).

In both cases the digital data is selected to play via the same method with Jriver’s app, Jremote, and the server has been configured for “original format” (PCM). The only difference being the source device’s “zone” output… (1) “this device”, (2) the WiiM.

I wouldn’t know how else to confirm bitperfect playback. The context of my query is that I’m considering a different streamer that has a USB output, and therefore my concern because if either case is delivering true bitperfect it is the one delivering higher volume, SPDIF coax??

I haven’t queried Jriver or WiiM yet because I considered the problem being my misunderstanding of USB vs SPDIF into a DAC, while the Jriver server and the WiiM are just doing their job. What would I ask? Should I absolutely expect the same volume if the streamer device could provide both outputs, USB and SPDIF? I would think so, but which volume would I end up hearing? That is, I also consider mysterious the volume setting ~80% (high gain) being extreme from a 7W (32ohms) headphone amplifier(?)

I’m not ruining anyone’s weekend, am I?
Cheers from The Avalon

 

[MaxwellsEq]

I can only assume both are bitperfect because of the general rule, “if you want bitperfect set the source volume to 100% and no EQ”

I suppose I can assume with greater confidence the DAP is delivering bitperfect because there is no way to control volume at the source. The iPhone is at the same volume only if set at 100%.

Unfortunately those tell you nothing about being bit-perfect. The fact that one is louder confirms something is "intervening" somewhere.

My RME interface supports a dedicated bit-perfect test. I can confirm no audible difference in volume through USB and S/PDIF when both routes are bit-perfect and using exactly the same audio file sourced off the NAS.