- A microfilter separates the voice and broadband signals that share a copper telephone line.
- Microfilters are needed on ADSL and FTTC connections that share the line with a phone service.
- On SOGEA and full fibre, where there is no shared analogue voice line, microfilters are not needed.
- Using the wrong number of microfilters, or none where needed, can cause connection problems.
- Modern faceplate filters can replace individual microfilters at the master socket.
A microfilter separates voice and broadband on a shared copper line, needed on ADSL and FTTC with a phone service. On SOGEA and full fibre, with no shared analogue line, microfilters are not needed.
Last reviewed: June 2026
What a microfilter does
A microfilter is a small device that separates the broadband and voice signals that share a traditional copper telephone line. On connections such as ADSL and FTTC, the broadband data and the telephone voice service travel over the same copper pair, using different frequencies. Without separation, these can interfere with each other, causing noise on calls and instability on the broadband. A microfilter splits the two so that each works without disrupting the other, plugging into a phone socket and providing separate connections for the phone and the broadband equipment. Understanding what microfilters do, and when they are needed, helps avoid connection problems on copper-based services.
The need for microfilters arises specifically from sharing a line between voice and data. As the industry moves towards services without a shared analogue voice line, the relevance of microfilters changes, which is an important part of the picture.
When microfilters are needed
Microfilters are needed on connections where broadband shares a copper line with an analogue telephone service, principally ADSL and FTTC where a phone service is present. In these setups, every device that uses the phone line, such as telephones and any other equipment plugged into phone sockets, needs to be connected through a microfilter so that the voice and broadband signals are kept separate. Failing to filter a device on a shared line can cause noise and instability. So for a traditional copper or part-fibre broadband connection with a phone service, microfilters are an essential part of getting the connection working reliably.
| Connection type | Microfilter needed? | Reason |
|---|---|---|
| ADSL with phone service | Yes | Voice and data share the line |
| FTTC with phone service | Yes | Voice and data share the line |
| SOGEA | No | No shared analogue voice line |
| Full fibre (FTTP) | No | Fibre to the ONT, no shared line |
When microfilters are not needed
Microfilters are not needed on connections that do not share an analogue voice line with the broadband. SOGEA, which provides broadband without a separate analogue phone service, does not require microfilters in the way ADSL and FTTC do, because there is no analogue voice signal sharing the line to separate. Full fibre similarly does not need microfilters, as the connection runs as fibre to an Optical Network Terminal rather than sharing a copper line with a voice service. As these services become more common, replacing the older shared-line setups, the need for microfilters diminishes, and households on them do not have to manage filters at all.
How many microfilters you need
On a shared copper line where microfilters are needed, the general rule is that every device plugged into a phone socket on that line should be filtered. This means each telephone, and any other equipment using a phone socket, needs a microfilter, while the broadband equipment connects through the broadband side of a filter. Using too few microfilters, leaving some devices unfiltered, can cause noise and instability, while the broadband connects through one. Getting the number right, with every relevant device filtered, ensures the voice and broadband signals are properly separated throughout the home, which is necessary for a stable connection on a shared line.
Common microfilter errors
Several common errors with microfilters cause connection problems on shared lines. Forgetting to filter a device, leaving a telephone or other equipment connected to a phone socket without a microfilter, can introduce noise and instability. Connecting the broadband through the wrong part of a filter, or daisy-chaining filters incorrectly, can also cause issues. Using a microfilter where one is not needed, such as on full fibre, is unnecessary, while omitting one where it is needed causes problems. Checking that every device on a shared line is correctly filtered, and that the broadband is connected appropriately, resolves many connection issues on copper-based services.
Faceplate filters as an alternative
An alternative to individual microfilters on each socket is a faceplate filter fitted at the master socket. This type of faceplate provides the filtering at the master socket itself, separating the broadband from the voice service for the whole installation, which can be neater than using a microfilter on every socket. Where a faceplate filter is fitted, individual microfilters on other sockets may not be needed in the same way, as the filtering is handled centrally. Many modern installations use a faceplate filter, which simplifies the setup and can improve performance by handling the separation at the point where the line enters the home.
Microfilters and the move to digital
The move from the old analogue telephone network to digital voice, and to services such as SOGEA and full fibre, reduces the relevance of microfilters over time. As the analogue voice service that shares the copper line is withdrawn, and as broadband moves to fibre or to data-only copper products, the shared-line setup that requires microfilters becomes less common. This means that, increasingly, households will not need microfilters at all. For those still on a traditional ADSL or FTTC connection with a phone service, however, microfilters remain necessary, so the need depends on the specific type of connection a household has.
Getting microfilters right
In summary, a microfilter separates the voice and broadband signals that share a copper telephone line, and it is needed on ADSL and FTTC connections that share the line with a phone service, where every device on the line should be filtered. On SOGEA and full fibre, which do not share an analogue voice line, microfilters are not needed. Common errors include leaving devices unfiltered or filtering where unnecessary. Faceplate filters offer a neater alternative, and the move to digital services is reducing the need for microfilters overall. Matching the approach to the connection type ensures reliable performance.
Frequently Asked Questions
What is a microfilter?
A microfilter is a small device that separates the broadband and voice signals that share a traditional copper telephone line, as on ADSL and FTTC. Without separation, the data and voice can interfere, causing noise on calls and instability on the broadband. The microfilter plugs into a phone socket and provides separate connections for the phone and the broadband equipment.
Do I need a microfilter with FTTC?
On an FTTC connection that shares the copper line with an analogue phone service, microfilters are needed, with every device plugged into a phone socket filtered, much as with ADSL. Alternatively, a faceplate filter at the master socket can handle the separation centrally. Where the connection is SOGEA, with no shared analogue voice line, microfilters are not needed.
Do I need a microfilter with FTTP?
No. Full fibre runs as fibre to an Optical Network Terminal rather than sharing a copper line with a voice service, so there is no analogue voice signal to separate and microfilters are not needed. The router connects to the ONT, and the filtering arrangements required on shared copper lines do not apply to full fibre connections.
What happens if I do not use a microfilter?
On a shared copper line where microfilters are needed, leaving a device unfiltered can introduce noise on calls and instability on the broadband, because the voice and data signals interfere. This can reduce broadband speed and reliability. Ensuring every device on the line is correctly filtered, or using a faceplate filter, resolves these problems on copper-based connections.
How many microfilters do I need in my home?
On a shared copper line, the general rule is that every device plugged into a phone socket should be filtered, so each telephone and any other equipment using a phone socket needs a microfilter, while the broadband connects through the broadband side of a filter. Using too few, leaving some devices unfiltered, can cause noise and instability.
Are microfilters still needed as services move to digital?
Their relevance is decreasing. As the analogue voice service that shares the copper line is withdrawn, and broadband moves to fibre or data-only copper products like SOGEA, the shared-line setup that requires microfilters becomes less common. Households on full fibre or SOGEA do not need them, while those still on traditional ADSL or FTTC with a phone service do.
