digital signal insight needed please

[WillW]

Hi, new here, and hoping to understand why, when I plug a DAC (Topping E30) into my 2015 Macbook Pro via USB, the Mac's volume controls still function.
My understanding, instinctive so likely faulty, is that a digital signal is basically a stream of 1s and 0s which the DAC converts to audible sound. By that reckoning, it ought to by-pass the Mac's internal DAC entirely, and therefore be inaccessible to any alteration between mac and external DAC. So how is the Mac's volume control still functional? How do you increase the volume of a load of 0s & 1s? Send them in UPPER CASE? Send them in bold? Seriously though - how does this work?
For the sake of trying out the DAC, I wound the Mac volume up to almost full, and the DAC did output sound into the amp (old but gorgeous Arcam Alpha 9). But has it been through the Mac DAC before it gets to the USB outlet? Presumably not, or it would be analogue already and the external DAC wouldn't work.
So, briefly, how is digital information increased in volume? And does that change the information going into the ext DAC? Volume control is the amp's job, isn't it?

 

[EdW]

Your Mac will be modifying the digital data stream by multiplying it by an attenuation factor. So as a trivial and simplified example 6dB attenuation would be achieved by dropping the least significant bit of the data and shifting the rest of the data one bit down replacing the most significant bit with a zero.
Your DAC gives best linearity and minimum noise by operating it at, or near max volume. So best not to use the Mac volume. This is particularly so since your Arcam has probably got an input sensitivity of ~200mV, some 20dB down on the nominal max output of the DAC. The effect of this is that you will not be using the full range of the volume control on the Arcam but this doesn’t matter too much. I think that the Arcam probably does not use an old style mechanical potentiometer as a volume control so channel balance should be good even at low settings.

 

[WillW]

Thanks. I don't really understand the technical stuff. You say best not to use the mac volume - that's my whole point really - there isn't a way NOT to use the mac volume when the USB DAC is connected. If I mute the mac volume, nothing goes to the DAC, no sound comes out of the DAC into the amp. As I said initially, I had thought that plugging a DAC into the mac USB would bypass the mac volume settings. It doesn't.

PS The Arcam does use old style volume control. It is motorised so can be operated from the remote.

 

[EdW]

Thanks. I don't really understand the technical stuff. You say best not to use the mac volume - that's my whole point really - there isn't a way NOT to use the mac volume when the USB DAC is connected. If I mute the mac volume, nothing goes to the DAC, no sound comes out of the DAC into the amp. As I said initially, I had thought that plugging a DAC into the mac USB would bypass the mac volume settings. It doesn't.

PS The Arcam does use old style volume control. It is motorised so can be operated from the remote.

OK sorry I didn’t make it clear set the Mac to max volume so that the data is sent across unattenuated. Muting the Mac volume will just send across perfect silence - just as you found out.
My Arcam FMJ32 from approx. the same era, has a remote control but the volume control knob doesn’t rotate under remote operation - it is purely a shaft encoder with the volume controlled in an integrated circuit block.

 

[WillW]

Thanks. So "modifying the digital data stream by multiplying it by an attenuation factor" doesn't alter the information being sent to the DAC..? It isn't "less pure" in some way? I'm not asking because I think I can hear a difference, I can't, my ears are too old. I'd just like to understand things a bit better.
The reason this came about is because my Fiio x5ii line out stopped working, so I started to think about a replacement. I didn't want to spend £400 on the new M11, as I have no use for blue tooth, wifi, apps and all the rest it now comes with. Just need a simple decent sound source. I already had the mac so thought I'd try the mac-DAC-amp route. As it turns out, the mac's own DAC is pretty good - the headphone-out to amp sounds ok, and the Fiio's headphone-out with the volume wound up works as well into the amp as the line out, so, much as I like new toys, I'm returning the Topping E30.

 

[boswell]

The E30 needs to be in DAC mode where volume doesnt work, the manual instructions are sparse, need to read it, multifunction button is the on/off button, only goddam button actually, good luck, great DAC

 

[WillW]

Yes I had it set to DAC mode. That's not really the issue

 

[Vini darko]

Simply put Volume over digital is just a code that tells the dac "this is loud , this is quiet , this is medium." Your macs volume control is just setting the code for "this loud" at a certian level from silance to max.

 

[bennetng]

So, briefly, how is digital information increased in volume? And does that change the information going into the ext DAC?

https://www.audiosciencereview.com/...depth-should-i-set-my-dac-to.8956/post-255104

Volume control is the amp's job, isn't it?

Yes, but partially. Read this to understand why. Read the whole article, don't skip. Applies to Mac and other OSes as well.
http://archimago.blogspot.com/2019/06/guest-post-why-we-should-use-software.html

 

[WillW]

Thanks. And down the rabbit hole I went
So, I kind of understand that the mac volume control isn't going to degrade the signal into the DAC, and that I should probably have the mac volume wound up to full to guarantee this. I am reassured.
But I'm putting the DAC idea aside for now, and continuing to use the Fiio connected by earphone jack to the amp while I research further into a new source component. Probably a tablet of some sort to DAC to amp.

 

[Soniclife]

But I'm putting the DAC idea aside for now, and continuing to use the Fiio connected by earphone jack to the amp while I research further into a new source component. Probably a tablet of some sort to DAC to amp.

You probably want a streamer of some sort, so that your laptop or phone work as a remote over your network, but don't need to be wired to your DAC, it's a nicer way to do it. Options start from super cheap like a raspberry Pi, up to options from traditional hifi manufacturers.

 

[Harmonie]

@WillW
Instead of "volume" (like an amplifier), you have to rather think "attenuation".
The more you attenuate the more you degrade the digital path of the mac.

 

[WillW]

Streaming isn't an option down this Devon lane, where the max broadband speed occasionally reaches 2.5MBs ! Even if it was, I prefer playing FLAC files stored on flash.

Ah yes - I get the attenuation / volume thing now. Thank you.

 

[EdW]

Thanks. So "modifying the digital data stream by multiplying it by an attenuation factor" doesn't alter the information being sent to the DAC..? It isn't "less pure" in some way? I'm not asking because I think I can hear a difference, I can't, my ears are too old. I'd just like to understand things a bit better.
The reason this came about is because my Fiio x5ii line out stopped working, so I started to think about a replacement. I didn't want to spend £400 on the new M11, as I have no use for blue tooth, wifi, apps and all the rest it now comes with. Just need a simple decent sound source. I already had the mac so thought I'd try the mac-DAC-amp route. As it turns out, the mac's own DAC is pretty good - the headphone-out to amp sounds ok, and the Fiio's headphone-out with the volume wound up works as well into the amp as the line out, so, much as I like new toys, I'm returning the Topping E30.

The topping e30 is a much better DAC than the internal Mac DAC and is a good match to the quality of the Arcam amp IMHO. If you want to turn the e30 into a streamer buy a Raspberry Pi4/4GB, a Raspberry Pi power brick, a 16GB SD card and a FLIRC case. Load Moode or Volumio on the SD card and proceed from there. The Raspberry Pi streamer will be indistinguishable in quality from a ’professional’ streamer costing many times more. You can either stream from the internet (difficult, I understand in your location) or plug a USB stick containing your music as FLAC files into the RPi4 and go from there

 

[bennetng]

Thanks. And down the rabbit hole I went
So, I kind of understand that the mac volume control isn't going to degrade the signal into the DAC, and that I should probably have the mac volume wound up to full to guarantee this. I am reassured.
But I'm putting the DAC idea aside for now, and continuing to use the Fiio connected by earphone jack to the amp while I research further into a new source component. Probably a tablet of some sort to DAC to amp.

You may try these test files as well:
https://www.audiosciencereview.com/...y-of-software-volume-control.5922/post-172865
"WASAPI exclusive mode" is a Windows thing, but just try if any of your Mac's volume control can properly decrease the volume of a.mp3.
Remember to turn down the amp when doing this test to avoid some nasty surprises.

 

[WillW]

I think the Raspberry system is not for me, getting further away from the simple single handheld solution I'd prefer.
I keep coming back to shall I / shan't I just buy the Fiio M11 and have done with it.

I do hear the difference between the mac output and the Topping E30, mostly better highs. Sadly, these days my hearing is a shadow of its former glory. Once I could hear bats and dog whistles, but no more. Partly it's age related, and partly, and most horribly, tinnitus. I have a continuous 7800hz tone in my ears, loud enough that listening to, say, Chopin's nocturnes, is no longer a pleasure, merely emphasising the tinnitus in what used to be the luscious dark silences between the notes. So, it's bigger music only these days.
The finer distinctions between equipment mean very little. I get more pleasure from depth and width of soundstage now than with detail and nuance. The Arcam excels here.

 

[Sgt. Ear Ache]

you're over-thinking this way too much. Set the Mac volume to 100% and forget about it. Use either the E30 in pre-amp/dac mode or the separate amp to set the volume. Personally, I'd set the amp to a volume somewhere slightly higher than the max you'd ever actually want to listen at and then use the E30 to set the listening level real-time.

(you could also set the Mac volume to slightly less than 100 - maybe 95% for instance - because there is some suggestion that 100% can introduce a tiny bit of distortion although that's not certain either. In the end, none of it is likely audible so don't worry about it))

 

[WillW]

Thanks. I just wanted to understand how a digital signal can be increased in volume pre-DAC. Thanks to some knowledgable replies to my original post, I now get it sufficiently to dismiss it. I'm reassured, as I said. For now, I'm ditching the Topping and carrying on with the Fiio straight into the amp.

 

[boswell]

Does the mac tell you the audio out on usb is to E30 specifically? Really mac volume shouldn't work if both ends are doing the usb thing correctly.

 

[WillW]

Yes it does. And yes, that's what I thought..