What is the ruling on acapella and fine-tuning? Acapella is when the vocal sound is used as musical instruments and fine-tuning is when digital methods are used to make the vocals sound more music like?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
In regards to acapella, due to it being a type of vocal singing which does not include musical instruments, people generally ask regarding its permissibility. Firstly, one must understand that it is still a type of singing and in regards to singing, many prohibitions have come. (However, I will try to address both issues separately viz. singing with instruments and singing without instruments.)
Firstly, regarding singing in general, Allah mentions in the Quran:
" And of mankind is he who purchases idle talks (i.e. music singing) to mislead (men) from the path of Allah without the knowledge and takes it by way of mockery for such there will be a humiliating torment ( in the hellfire )
(Surah Luqman, Ayah 6)
Hazrat Abdullah Ibn Masood (r.a) was asked regarding this verse and he replied, “It is music, by the oath of that being there is no deity except Him.”
Other Sahabah had similar opinions also. For example,
Ibn ‘Abbās (Radiyallāhu ‘Anhu) says, “It is singing and the purchasing of singing women.”
We see from the above ayah that singing has been prohibited and the reason for this is because it takes one away from the path of Allah and makes one heedless of the hereafter.
Apart from the above ayah, we see clear warnings from Ahadith about the punishment of singing and music:
Imran bin Husain (r.a) narrates that the Prophet s.a.w said ‘This Ummah will experience the swallowing up of some people by the earth, transformation of some into animals, and being rained upon with stones’. A man amongst the Muslims asked: ‘O Prophet of Allah! When will this be?’ He said: ‘When female singers and musical instruments appear and alcohol will be consumed’. 
The above Hadith clearly warns us about singing, the use of instruments, the consuming of alcohol and the punishment for such actions. This is just one example of a warning of the bad effects of singing and music etc. hence one realises the severity of such actions generally.
Now, in regards to non-instrumental music or vocal music, there are similar issues which will be addressed below.
In general, even if acapella does not include musical instruments and it is just mere singing, in today's time, due to all kind of fitna and social media we are surrounded by and face on a daily basis, one can say it still carries the same disastrous and poisonous effects of music.
A typical example is that even though the singing is vocal, it doesn't just end there, rather you have violent videos or dancing that comes with it. At times, such videos promote haram and you have the opposite gender singing which spiritually has a huge effect on one's Imaan. It won't be wrong to say it is like playing with fire.
At times, it becomes difficult to differentiate between acapella and music produced from musical instruments to the extent at times we see that such vocal sounds have become background music for many Islamic lectures, talks or short clips etc. and thus being a means of entertainment and a substitute for music and having similar effects as normal music.
In some cases, we find that it has lead people to listening to normal music (instrumental music) because they can't tell the difference between the two.
In conclusion, one should abstain from such music especially in this time of fitna. In my humble opinion, acapella will fall under the category of the above ahadith, therefore, vocal music of this type will not be permissible.
Only Allah knows best
Written by Maulana Belaal Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sunan- at -Tirmizi (pg 45 vol 2 (Qadeemi kutub khana print)