What to broadcast during the show
Mixing for Assistive Listening
There are several approaches to creating an Assistive Listening mix. Whichever one you choose, it is vital that your microphone technique captures speech that is clear and free from noise and reverberation.
The best results are obtained when each actor has their own close-talking microphone. Be sure to avoid picking up the rustling of clothes and plosives. Distortions which are inaudible when the signal is output through a PA can be very unpleasant when output through hearing devices.
Top tip: If your venue hosts touring productions, plan ahead for what and how they will deliver the Assistive Listening mix.
To deliver the best possible customer experience, we recommend creating a dedicated Assistive Listening mix which is produced as an integral part of the sound design process of a show production. This allows the balance of all sound elements to be crafted so speech is clear, sound effects are audible but not overwhelming, and music does not mask dialogue.
The most obvious approach is to simply route the main PA mix to the Assistive Listening system.
In a simple production, for example where there is only dialogue, this could be acceptable. In this case, the main mix should be produced in the same way as a dedicated AL mix, as described above.
If it is not feasible to create a dedicated Assistive Listening sound design from the onset of production, a compromise could be to create sub mixes (also known as “buses”) for different categories of sound. It is then possible to balance the levels of dialogue, music and effects to create an Assistive Listening mix that is output from the sound desk separate from the main mix.
Whichever approach you take, check the Assistive Listening mix during rehearsals and pre-show sound checks and fine-tune if necessary.
Auracast compliance
Did you know? Auracast compliant transmitters
For a transmitter to be Auracast compliant it must broadcast a Standard Quality (SQ) stream. This is to ensure that hearing devices with small batteries and limited processing power, such as hearing aids, are always able to receive the audio.
A transmitter can optionally broadcast a High Quality (HQ) stream in addition to the SQ stream. For people listening with earbuds or headphones this could give a noticeable improvement in the sound quality of music.
SQ streams must have a sampling rate of 16 kHz or 24 kHz. We would recommend 24 kHz. HQ streams have a sample rate of 48 kHz. For context, CDs are stereo with sample rate of 44.1 kHz.
Additional broadcast options
The simplest possible broadcast is a mono stream at Standard Quality. There are several ways you can deliver an even better experience to more people.
Broadcasting a stereo mix can create a sense of space. Spatial separation improves speech intelligibility, makes sound more immersive and can help with localising musical instruments. If the main mix includes stereo elements then people with hearing loss should be able to experience those too.
Auracast systems must transmit a standard quality (16 or 24 kHz) stream to ensure compatibility with hearing aids (see Auracast compliance). A High Quality stream can broadcast higher frequency sounds. This is unlikely to provide any benefit for speech but can deliver a richer music experience for people using headphones, earbuds and loudspeakers. There are no special requirements to create a High Quality stream. Some transmitters can produce both from the same input feed.
For blind and partially sighted customers, the ability to access an Audio Description (AD) stream using their own devices removes the friction of needing to borrow a device. For people who use a screen reader this could make the process much smoother.
An AD mix is simple to create.
If people need to access both AL and AD, there are a few options, each with pros and cons. At present the simplest is to use a third transmitter channel to broadcast a combined stream. This could be derived in the sound desk, using a summing amplifier, or within the transmitter.
Another approach is to use two receivers and mix the signals, or listen to AL and AD signals at the left and right ears.
We think manufacturers could update firmware to allow the mixing to be done at the receiver end. This could even give users the ability to adjust the balance between the two streams.
You can support international audiences by providing simultaneous translations into other languages, with each being broadcast on its own Auracast audio stream.