BRIC-HQ1 (High Quality 1)
This algorithm keeps delay low (around 1/10 second) but allows for full fidelity (15 kHz) audio transmission. It delivers music or voice audio equally well and runs at a data rate of 28 kb/s. This mode also allows dual mono transmission, so that two independent audio signals (using twice the network bandwidth) can be sent to the same location. HQ1 settings offer choice of mono, dual mono or stereo.
BRIC-HQ2 (High Quality 2)
This mode minimizes artifacts and encodes speech and music equally well, providing a 12 or 15 kHz fidelity signal over 24 kb/s of network bandwidth. BRIC-HQ2 also allows for stereo operation at the lowest data rate of 24-30 kb/s, making stereo over a single modem connection possible. BRIC-HQ2 has moderate delay of about 1/3 second, which is in the range of many ISDN codecs. HQ2 settings offer choice of mono 12K, mono 15K, stereo 12K or stereo 15K. Selecting 12K further reduces artifacts.
BRIC-ULB (Ultra Low Bitrate)
This mode is designed for speech transfer only but has a remarkable compression ratio of around 25:1, allowing it to deliver 7 kHz at an astonishingly low bitrate (around 14 kb/s). The voice quality of BRIC-ULB is comparable to the old codec standard G.722 (7 kHz), but uses less than 1/4th the amount of data.
G.711 and G.722 coding algorithms for compatibility with SIP-style VoIP phones.
ACCESS's linear mode digitizes audio to 16 bit samples. It does not compress the audio further, but packetizes a frame of audio samples and transfers them across the network uncorrupted. Analog audio is sampled at 48 kHz, providing 22 kHz frequency response. If AES3 Input/Output is used, ACCESS can utilize 44.1 kHz and 32 kHz sampled audio.
ACCESS offers the FLAC (Free Lossless Audio Compression) algorithm for those who wish to conserve bandwidth without sacrificing audio quality. Since FLAC is lossless (the exact PCM word applied to the encoder is extracted from the decoder) there are no concerns about artifacts or immunity to further coding in the link.
FLAC utilizes a variable output encoder, and data rate will rise and fall based on the ability of the encoder to compress a particular frame of audio. For example, during complete silence FLAC outputs less than 1/10th the data of linear PCM, while encoding full-spectrum, full scale white noise results in data rate slightly higher than PCM. On average audio, FLAC will typically remove 30-40% of the network data when compared to linear.
FLAC encodes analog audio at 48 kHz with 16 bit resolution. If AES3 In/Out is used, FLAC can utilize 44.1 kHz or 32 kHz sampled audio, further conserving bandwidth. Frequency response and all other specifications are identical to linear, with a slightly longer (5ms) delay.
While BRIC-HQ1, BRIC-HQ2 and BRIC-ULB are more than suitable for the majority of remote broadcast applications they are not what some would consider "STL quality" audio.
In order to provide both 20 kHz STL quality audio as well as future compatibility with codecs from other manufacturers, Comrex has implemented MPEG-4 AAC, MPEG-4 HE-AAC, MPEG-4 HE-AAC v2, MPEG-4 AAC-LD and MPEG-4 AAC-ELD licensed by Fraunhofer IIS for ACCESS. These algorithms are now included with all new ACCESS codecs.
For applications that require reduced bandwidth but excellent audio quality, ACCESS can utilize the highly regarded AAC coding algorithm (licensed by Fraunhofer IIS) to provide near-transparent stereo audio at a data rate of 128 kb/s or lower.
To further reduce network bandwidth requirements, HE-AAC combines the coding power of AAC with Spectral Band Replication to reduce the data requirements for high frequencies. HE-AAC is typically deemed to sound nearly as good as AAC at lower network bandwidth. HE-AAC is the standardized version of the algorithm known as AAC-Plus.
The HE-AAC v2 algorithm further increases the efficiency of HE-AAC by utilizing parametric stereo encoding. This results in a lower bit rate for stereo signals.
AAC-LD requires higher data rates but provides near transparent voice and music with low delay.
AAC-ELD combines the best aspects of low-delay audio coding with Spectral Band Replication to reduce bitrate. This combination creates a coding algorithm that is uniquely suited to real-time IP transmission. Using AAC-ELD with ACCESS allows full-fidelity high quality audio transmission at a data rate that easily fits into satellite and 3G wireless upload channels. One way ACCESS transmission delay using AAC-ELD is an easily-managed 50 milliseconds.