Choosing a bitrate

Every figure below assumes our encoder. The same bitrate on a standard encoder sounds materially worse, which is the whole reason we exist. If you are carried at 32 kbps today and it does not sound like the description here, that difference is what we are talking about.

What comes out also depends on what goes in. A well-produced, sensibly processed feed will reach these descriptions comfortably. A poorly processed one will not, whatever encoder handles it, and we can show you where your chain sits.

Please note the guidance below is necessarily subjective. We have refined our view of what is acceptable through feedback from stations, listeners, competitors and colleagues across the industry. It rests on two things: what a station expects, balancing budget against quality, and how important a given area is to that station – a core broadcast area, or a distant one that simply extends coverage for the occasional out-of-area listener.

DAB+: what we would recommend

	Budget-led	Balanced	Quality-led
Primary area	32–40 kbps	48 kbps	64 kbps
Secondary area	24 kbps	40 kbps	48 kbps
Trial or tertiary area	24 kbps	32 kbps	40 kbps
Speech service	16 kbps	32 kbps	48 kbps

Speech-only services have a distinctly different bitrate profile which is based more upon the quality a service will accept, and we find the marketplace relevance is less significant.

What each rate sounds like

16 kbps: Clear, intelligible speech. Not suitable for music.
24 kbps: Reasonable quality music, in stereo. Good for extending reach or testing a new market. A rate at which most encoders would give up on stereo altogether. Fine for noisier, higher-speed in-car listening – motorways, vans and lorries.
32 kbps: Reasonably good stereo music, comfortable for extended listening in a non-discerning environment.
40 kbps: Good quality, with some minor impairments audible in a more discerning environment.
48 kbps: Good to excellent, with only minor impairments.
64 kbps: Excellent. The rate for stations that want the best available.
Above 64 kbps: Available, but we do not expect many stations will need it with our encoder. We would rather tell you that than sell you capacity you will not hear – you will likely need a controlled listening environment to tell the difference above 64 kbps, and typically it will be shortcomings in the contribution chain, such as studios, processors or similar, that are causing degradation at 64 kbps.

What we mean by the terms

Budget-led: Carriage cost is the deciding factor. Many volunteer-run and community services sit here, and there is nothing wrong with that. We are pleased to be able to help such stations get better audio quality within their budget, or expand to adjacent areas at a carriage price they can actually afford.
Balanced: You want the service to sound good, within a sensible budget.
Quality-led: How you sound is part of what your station is. You would rather pay for the capacity than compromise. You have spent serious money on a serious studio and processor, so why let it down with your DAB bitrate?
Primary area: Where your core audience is and where most of your listening happens.
Secondary area: An adjacent or expansion area that matters, but less than the primary one. Listeners will accept a slight reduction as they know they are outside the primary editorial area, in the same way that FM tails off as you leave the main service area.
Trial or tertiary area: Somewhere you are testing, or where the audience is small enough that reach matters more than fidelity. Typically listeners will be travelling through at speed, or will have reached their destination and will shortly return to your primary service area.

DAB or DAB+?

This is primarily a reach and cost decision rather than a quality one. DAB+ sounds better at all bitrates below 128 kbps, but the oldest DAB radios cannot decode it at all. The main question is how many of the sets in your area are DAB-only.

In our experience that varies enormously across the UK. Parts of Leicestershire still appear to have a high proportion of DAB-only receivers in use, while in London the proportion is very low. Neither figure would be a safe guess from the other. If you are weighing this up for a particular area, ask us and we will tell you what we see, or the local multiplex operator should know their area.

DAB (MP2) needs considerably more capacity for the same result, and its quality climbs steeply above 96 kbps. If you are carried in DAB and quality matters to you, we would not recommend anything below 112 kbps, and 128 kbps is where it belongs.

Our MP2 encoder is unusual in remaining under active development. Most have had little attention in twenty years while the industry’s effort moved to AAC, which is understandable but leaves them designed around the very limited processing power of the 1990s. That shows most clearly at the bottom of the range, where conventional MP2 encoders produce little worth listening to – the allocation becomes unstable and collapses, with a dramatic loss of quality below 48 kbps.

32 kbps: Intelligible mono, roughly comparable to a cassette recording. A tertiary area for a smaller station reaching listeners on older DAB-only receivers.
40 kbps: As above, with the artefacts noticeably less intrusive.
48 kbps: The lowest we would recommend for a primary area for a budget-led station, where a large part of the audience is on older DAB-only sets.
64 kbps: Good mono for a primary area, or stereo at reduced quality.
80 kbps: Suitable for a primary area where capacity cost is a real constraint.
128 kbps: Near CD quality stereo. At this rate we typically measure and hear our MP2 cleaner than FDK-AAC at the same bitrate.

DAB+: what we would recommend

What each rate sounds like

What we mean by the terms

DAB or DAB+?

Not sure which rate fits your station?