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Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

RE: Did you finish your posting?

Your question have may been easier for me to answer if you had told me what you want to do with the output from your Galaxy Note 4. Are you feeding headphones directly or do you want it to feed into an audio system via a pre-amp or integrated amp?

You are asking two things that are not the same, one is volume output, the other quality output.

Basically the volume output from any digital file, MP3 or CD has a maximum level of 0dBfs ( zero decibels, full scale). What that means in voltage output terms depends upon the DAC. This is conventionally 2V although some DACS provide higher outpus. The importance of this depends upon what you wnat to do with it. If it is 2V ( doesn't matter if it's MP3, CD, hi-rez, DSD) then normally it will need some kind of attenuation as it will be too high for many headphones and power amplifier inputs. That's why there is a volume control on the preamp/integrated amp.

So I gather that your MP3s are too quiet for whatever it is that you do with your Galaxy Note 4. Well, it's a tablet so it may not have the conventional 2V output (I don't know) and may require some kind of external device to raise it if it is to drive e.g low sensitivity/high impedence headphones or a standard line stage input. So, in answer to you first question, virtually all DACS will provide at least a 2V output. DAC/headphone amps like the AQ Dragonfly may not as they are specialised. For example the Dragonfly Black has a lower output than 2V. However the Red version is OK on this aspect.

However it may be that your MP3 files do not have a maximum sound level for some reason of 0dBfs ( everything else being equal). They will therefore sound quieter than an audio file that does. In fact in real life good recordings will have a maximum output level below 0dBfs to avoid clipping. Furthermore recordings with a wide dynamic range will sound quieter on average so that the high peak sound levels can be at or around 0dBfs. Anyway the variations of maximum sound levels of the files should usually be dealt with by the preamp not the DAC. That's what it is for. Yes, some DACS have volume controls and can act as pre-amps. However if for some reason more than 2V is required you normally do need an active pre-amp.

So, on to the second aspect of your question, quality.

Upsampling cannot add information. An MP3 audio file has thrown away some information and it is not possible to get it back. So upsampling will do nothing on this account. All that upsampling does is allow the placing of the digital filter further out of the audio band which minimises some of the audible abberations of the filter e.g. pre-ringing. It does not improve quality per se but can improve the listening experience in some circumstances. If you want CD quality then you need to have files of 16/44.1 without any lossy processing i.e. not MP3s as they cannot be improved in reality. However, as I say, upsampling may improve your experience but I would not rely upon it when using lossy files.

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