Audio sample rate can be vexing for voice-over localization professionals. Why? Because getting it wrong can mean video dubbing files that don’t synchronize properly, or an IVR system that doesn’t work at all. Fortunately, it’s not terribly difficult to get it right – if you know what you’re doing.
This post will explain what audio sample rate is, and what multimedia localization professionals must do to get it right on audio and dubbing projects.
[Average read time: 3 minutes]
To record audio, digital systems take measurements of sound waves at certain intervals – that is to say, they do this a certain number of times per second. Each one of these discrete measurements is a sample – therefore, the audio sample rate is the number of these measurements taken per second of audio recorded. In general, the more samples taken per second, the higher the quality of the audio, just because the larger number of measurements gives the audio greater accuracy.
Sample rate is represented in Hz. A standard sample rate is 44,100 Hz – that’s audio that’s recorded at 44,100 samples per second. That figure can also be represented as 44.1 kHz, or 44.1 thousands of Hz. This rate was adopted for CDs, and was carried on to the first MP3s as well, and for this reason is still the go-to for most voice-over recordings. However, there are several sample rates in use today. Audio for video (including dubbing voice-over) uses a sample rate of 48,000 Hz (or 48 kHz), which was adopted early on because audio at this rate can be synchronized to film and video in the US and Europe. Likewise, the audio used in phone directories is often recorded at 8 kHz because it works with the frequencies used in phone lines.
The following screen shot is of a sound wave from an 8 kHz recording – each dot on the wave represents a distinct audio sample. Note that this sound wave represents only about 0.005 seconds of the full voiceover audio file.
For one big reason – because different applications and players require audio recorded at a specific sample rate. Videos are the most common example. Because most video editing systems require audio audio recorded at 48 kHz, they won’t interact well with audio recorded at any other sample rate – serious synchronization issues start to appear in post-production, in fact.
Same goes with many legacy e-Learning and LMS systems, multimedia players, phone systems, public service announcement systems – and just about any other audio and video delivery platform. Most of them have specific sample rate requirements.
There are four things that audio and video localization professionals have to keep in mind.
If you don’t get the specs right, your final audio will not integrate properly. If you deliver 44.1 kHz audio for a video localization project, your client will almost certainly not be able to use it. Yes, audio can be converted from one sample rate to another, but this process is tricky and time-consuming, especially when going from 44.1 kHz to 48 kHz. It can also mean a loss of audio quality – requiring that you re-record.
It costs the same to record in most sample rates, so this information isn’t necessary to get a quote. For example, if you get a quote for an animation dubbing project and then find out you need to deliver the audio in 44.1 kHz, that won’t affect project pricing.
Not only are conversions difficult, but some projects also require recording with a higher sample rate. For example, some clients require 96 kHz for a higher source audio quality, and then converting down to 48 kHz for the deliverable audio. If you’ve recorded at 48 kHz, you won’t be able to deliver the 96 kHz audio that your client has requested without serious quality issues.
Some animation software prefers audio in 44.1 kHz – for example, many audio projects recording for output from Adobe Flash run into this issue. Likewise, many legacy e-Learning platforms use 22 kHz audio, in part because it requires less storage and bandwidth. And many applications have licensed players that require a different sample rate altogether. Expect to see the full gamut of sample rates, but don’t be afraid of them – remember that a professional studio like JBI will be able to support all of them.
Fortunately, most multimedia localization clients will have specs for the audio recording sample rate they need for their deliverables. For clients that don’t, you can usually just match the sample rate of their source audio – this is a service we perform at JBI Studios. Finally, it’s always good to run the audio sample rate – along with a full suite of recording specifications – by your client before production begins, to make sure that there won’t be issues during delivery or implementation. Yes, that requires getting information up front from a client that may not know much about their audio or video files, and possibly delaying production – but this step is critical to ensuring that your projects deliver on time, on budget and with the highest quality possible.