Of the twenty one senses that we have, hearing plays a large role in how we experience the world we live in. When it comes to video, humans tend to accept the limitations of the current generation technology. Remember when monochrome TVs were widely adopted? Mom remembers. However, we always expect clean, crisp audio from our entertainment/news platforms. Bad sounding media is often unforgivable as compared to poor image quality. Herein lies the need to ensure consistent great quality audio reaches your listeners. Let’s check the considerations audio engineers in your plant can contribute to the highest possible audio quality and consistency.
Audio media goes through two major processes during its creation, audio production and audio processing. Production involves the activities and equipment used to capture or create sounds. This includes audio design, mixing, editing, dubbing, applying various sound effects and balancing sources. Audio production is beyond the scope of this topic but will be referenced to as it comes before the audio processing chain.
The audio processing chain refers to the activities and processes to give your audio a particular desired sound. That means that the sound from your production site has a particular mood and feel. This is achieved by the technical manipulation of the audio signal. Processing is based how you want your audio to impact your listening audience, an interesting scientific study called psychoacoustics.
Quality
Audio engineers need to ensure the best signal quality of the audio that is produced from the production sites (they may be audio labs, recording studios, FM and TV studio etc) and this process starts from the infrastructure used to capture and transmit the sound. Isolation and acoustic treatment was covered in a previous post, beyond that we have the transmitting elements; cables and connectors. XLR cables should be fabricated well as and the audio cable should be of high quality. I’ve had instances of cables I bought having rusted sleeves! So be wary of those Luthuli Avenue stores and pick the right brand. High quality connectors should be used for the best sounding audio. The popular Neutrik connectors should suffice. High quality microphones for better sound capture should be used. However, great sounding audio doesn’t come cheap.
Testing your connections can be quite easy as long as you do not have complicated cable paths. Also avoid running them alongside power cables to minimize interference. Test for any shorting of the cable elements (hot, cold and sleeve/ground) using a continuity test and resistance along the sleeve should be as low as possible. The rusted sleeve I described earlier had high resistance. Testing for audio in a large plant after all cables are terminated may be a grueling task therefore it is best to plan early on testing while terminating the connections to ensure you are satisfied at each step.
Now check your equipment for any distortion from clipping before getting the signal to the audio processor, in an FM plant the standard equipment before the processor are:
- Microphone preamps
- Console summing amplifiers
- Communication devices such as phone systems, remote links
- Analog-to-digital converters
- Stereo profanity delay
- Computer sound cards
Consistency
Audio quality MUST be ensured before processing as manipulating bad audio to give you desired results is a worthless effort. In the audio processing chain the sound engineer can perform a set of operations to fine-tune the signal. For best results use linear uncompressed audio formats such as WAV as compared to compressed formats like mp3. A digital sound processor may be added to your chain to perform the following operations:
- Multiband compression
- Stereo expansion
- Equalization
- Automatic gain control
Multiband compression is a form of dynamic range compression. This range compression is performed to either amplify low levels or reduce higher levels. It is important, say in traffic, that the low levels does not get lost in the background, and high levels aren’t too uncomfortable for listeners.
In the automobile, dynamic range cannot exceed 20dB without causing problems
Automatic gain control is usually the final step to the output. In electronics, it is a closed-loop circuit that provides a feedback loops allowing for a controlled output despite variable input amplitude. This is used to ensure consistent volume of the audio signal. From Figure 2, the signal to be gain controlled goes to a diode and capacitor, which produce a peak-following DC voltage.
- Studio Transmitter Link
- Transmitter
- Filter and feeding equipment
- Antenna
The 4 equipment were covered in a previous post.
Conclusion
While the nuances of audio may not be fully appreciated by mass audiences, it plays a large role in ensuring a consistent ‘image’ or ‘brand’ of your particular production plant. This goes a long way in attracting and retaining consumers in the constant competition spanning many disciplines be it film production, game design or hardware manufacturing. This post serves to quickly summarize the important processes giving you somewhere to start when diving into the wide field of audio.