Use of originating volume control in digital stream?

[ozzie]

I have followed this site for some time, but this is my first post. While I am a very old hifi nut, I am a veritable novice in digital streaming. On reading most of the tests on this site I recently purchased a Topping D30 and I am extremely happy with the results. Even my old ears can detect an improvement from my Airport Express direct analog, to the introduction of the D30 in the signal path. (I have a good amp and very good speakers).

I stream ALAC from iTunes on my Mac, via a 1st generation Airport Express, via the Topping D30, to my analogue Amp. I control what I play via the Apple Remote app on my iPad.

My question is: the volume control in the iTunes volume slider can control the output volume from my amp. How does this happen?
How is the iTunes "volume setting" carried in a digital bit stream, that I thought just contained bits from the ALAC source?

PS I have set the iTunes to 100%, as I read somewhere on this site that was recommended, but I cant find that post.

 

[RayDunzl]

My question is: the volume control in the iTunes volume slider can control the output volume from my amp. How does this happen?
How is the iTunes "volume setting" carried in a digital bit stream, that I thought just contained bits from the ALAC source?

Basically:

The digits in a stream represent relative voltage levels, and if you graph the numbers, it "looks" like an analog wave., just like you'd see on a scope hooked up to the speaker leads.

To vary the volume (amplitude) represented by that stream of numbers, all of the sample values are multiplied or divided.

Divide by 2 and it is a 6dB reduction, for example. Doesn't have to be an integer amount in the multiplicand or divisor.

The DAC turns the stream of sample digits into an analog wave of varying voltage (looks like the graphed numbers above) for the amplifier to amplify.

 

[ozzie]

Basically:

The digits in a stream represent relative voltage levels, and if you graph the numbers, it "looks" like an analog wave., just like you'd see on a scope hooked up to the speaker leads.

To vary the volume (amplitude) represented by that stream of numbers, all of the sample values are multiplied or divided.

Divide by 2 and it is a 6dB reduction, for example. Doesn't have to be an integer amount in the multiplicand or divisor.

The DAC turns the stream of sample digits into an analog wave of varying voltage (looks like the graphed numbers above) for the amplifier to amplify.

Thank you for the explanation. So does it matter what the volume slider is set to in iTunes? Will it have any bearing on quality?

 

[RayDunzl]

Thank you for the explanation. So does it matter what the volume slider is set to in iTunes? Will it have any bearing on quality?

Within the range you are likely to use it, it shouldn't have noticeable deterioration.

 

[RayDunzl]

Here's a view of 60dB attenuation. That's a lot.

Check the scale on the left.

 

[ozzie]

Within the range you are likely to use it, it shouldn't have noticeable deterioration.

Thank you yet again for your help. I am beginning to understand.