Draft a mail regarding this and warn for such loud speaking at workplace and advise them use intercom facility services, if they are speaking apart from professional work then warn them through the mail keeping CC to your HOD or Management head.
See the nature of production/process and whether raised voices are because of noise of machines/processes etc.
Are there complaints about noisy atmosphere?
Making people talk less loudly is not a priority for a new HR.
Take time to understand and then act in phased manner in consultation with HoD/line managers etc.
Being apparel industry the noises of sewing machine is inevitable and when the Supervisor or worker want to communicate to each other there is no other option except to raise the voice and talk. While your effort to bring in work discipline is understood, HR should also analyze the nature of business process. Apparel Industry is not a corporate office. So you can look at implementing related measures like safety in work place, cleanliness, welfare for workers like Mediclaim etc.
Also when you are new to work it is not advisable to implement corrective measures of any sort immediately as workers tend to agitate and will no co-operate. First important thing is to develop good relationship with all employees and then to implement corrective measure gradually.