For everyone who has been in the broadcast engineering field for a while, terms such as VU meters, PPM (Peak Program Meter), Loudness Meters, PFR (Peaks of Frequent Recurrence), Noise, Distortion, Phase, THD (Total Harmonic Distortion), Pre-Emphasis, and De-Emphasis all bring back some type of memories. Some of these are good, and some not so good. Some of those terms are still applicable, and the goal remains the same—to provide listeners with the most accurate representation of the sounds that were recorded/detected.
With the advent of digital audio, many hurdles have been removed while others have just been placed at different locations on the track. I would argue that broadcast audio has never been cleaner and that its dynamic range and frequency response are certainly remarkable. However, multiple channels of audio per program combined with many different distribution options has left a vacuum in the area of monitoring and evaluating digital audio, at least until recently.
Linear Acoustic, a manufacturer of digital audio products and technologies, has taken the lead by offering the LAMBDA (Linear Acoustic Monitor for Broadcast Digital Audio) product to allow monitoring and evaluation of both multichannel audio and metadata content in the professional broadcast environment.
The LAMBDA occupies 2 RU and weighs approximately 10 pounds. The unit has an operating voltage range of 100 to 240 VAC at 50 to 60 Hz. Power consumption is 45 watts maximum, and the operating temperature spec is from zero to 50 degrees C, in an environment of up to 98 percent relative humidity (noncondensing).
|The Linear Acoustic LAMBDA audio/metadata monitor |
The rear of the unit is loaded with I/O, including dual power supply connections, 16 BNC's for discrete AES inputs and loop-outs, two BNC's for SMPTE 292 input and loop-out, USB, Ethernet, two DB-9 connectors for GPI/O and metadata connection, and finally, two XLR connectors for analog monitoring of Lt/Lo and Rt/Ro and a BNC for AES output of LtRt/LoRo.
The front of the unit is very attractive, and features two-way speakers driven by four digital power amplifiers, using Linkwitz-Reilly crossovers. There's also a headphone jack and a large long-life vacuum fluorescent display bordered by two navigation clusters for operation and control.
The LAMBDA is designed to monitor baseband PCM via AES and HD-SDI by arranging the sources into groups that may be stored as presets. It provides AES outputs of all 16 embedded audio channels when HD-SDI input is selected or an active loop-through when the AES inputs are selected.
Metadata supplied as RS-485 serial or VANC formats can be displayed and even applied to the audio signals to simulate its effect before transmission. The LAMBDA provides ITU BS1770 loudness metering and has adjustable integration times. As an option, the unit can accept Dolby E/Dolby Digital. Linear Acoustic's e-squared decoding can be provided for metering and output of discrete audio channels and metadata. Any channel, pair, or downmix can be monitored through the internal speakers, front headphone jack or rear output downmix/monitoring output XLRs.
ITU BS-1770 Loudness metering is standard on the unit, and along with a numerical value, there is a level-indicating line that floats across the audio metering screen for a quick overview of loudness level. In addition to the ITU level, dialnorm values are displayed in a similar manner, when data is present. All metering is available via Ethernet connection for remote monitoring.
The LAMBDA sampling rate is 48 kHz, and the frequency response (outputs) spec is 20 Hz to 20 kHz. The speaker output levels are specified at a 98 dB SPL at one meter, 160 Hz to 20 kHz, and 85 dB SPL at 120 Hz. The headphone output is at +12 dBu max into 600 ohms, and the internal speakers are muted when a headphone plug is inserted. Latency is specified at less than one ms for PCM audio, 33 msec for AC-3 and Dolby E (NTSC), and 40 ms for Dolby E (PAL). Metadata input can be either via an RS-485 9-pin D connector, or it can be extracted from the VANC portion of HD-SDI signals.
I couldn't wait to get the LAMBDA up and running, as all I've heard for the past two years is "dialnorm-this" or "dialnorm-that." Like most broadcasters these days (I suspect), we're kind of eating bologna sandwiches around here when it comes to obtaining a lot of new test/monitoring gear.
The first order of business was to mount the LAMBDA in my television station's new HD syndication ingest/playback area, which provided close proximity to many different discrete 5.1 AES sources, as well as several HD signals (via satellite). Using both HD-SDI and three discrete AES channels, hook-up was quick and easy. With just a few short BNC cables I connected HD-SDI from my router, as well as three AES channels from a monitoring d.a., to the unit.
When I powered up the LAMBDA, the display made a very crisp picture. And after a minute or two, I discerned that the knob and menu buttons on the right were mostly for volume control and quick monitoring functions, while the knob and menu buttons on the left were for navigating the menu tree, which include setup, presets, I/O, communication and system.
The first order of business was to select the type of input I wished to monitor. For testing purposes I decided that I should have three presets: one with HD-SDI (embedded) plus metadata, one with BNC AES (discrete 5.1) plus metadata, and a preset with just AES stereo.
I figured that configuration would be done in the "Preset" menu. To confirm that fact, I referred to the included manual. After just a few minutes, the "menu tree" became fairly clear. To program or change a current setting on the unit, all one has to do is rotate the knob on the left side of the unit to change options. When a selectable function is available, an asterisk appears beside the "new option". To accept the new setting, you simply press the "right" button on the navigation pad.
After about five minutes, I'd created my three presets and named them with my personal information. Again, once you become familiar with the menu tree it's easy to bounce around through it with ease. Creating the presets was kind of a cool trick; however, it became evident that I had a little more work to do. I could see six channels of audio, but on the display the channels were labeled with generic numbers. Going into my preset menu a bit further, I learned how to label the channels properly on the display. For example, for 5.1 (six channels) there was a label to assign Lf, Rf, C, S (for Sub), Lr and Rr under each channel's meter. Once I had routed and labeled the channels for each preset, I started listening to the unit. The sound quality was very good. Using the left knob, you "roll" a curser under the channel you wish to listen to, and just leave it for a second or so. To monitor all of the channels, roll the cursor off of the screen and leave it. You will hear a mix of the active channels.
Bar graph metering on the display is very straightforward, and the unit constantly displays the ITU loudness level on the bottom right of the display. In addition, there is a traveling horizontal line that tracks the ITU level across all channels, giving a constant graphical indication of the loudness level.
After becoming familiar with the unit, I decided it was time for the moment of truth: I wanted to detect, display, and monitor audio metadata. However, being unable to detect metadata on my own, I placed a call to Linear Acoustic. They confirmed what I had guessed. If the data is there, the LAMBDA will show it to you. It was obvious that there was no dialnorm present, as the window in display indicated no DN value present (- -). I tried selecting HD-SDI inputs from different sources: our Tiernan HD receiver locked on NBC, our rainfade backup NBC HD receiver and syndicated feeds from CBS distribution. There was no data to be found, at least in the VANC portion of the HD-SDI signal. It seems I had to educate myself further, and dig a little deeper.
After talking to the fine folks at NBC, I learned that currently, the only metadata available to this affiliate is via the data port on the back of the Tiernan. RS-485 metadata can be detected on the rear of the Tiernan; however the RS-422 option must be turned on and the PIDs must be present. (I learned from NBC that in the near future metadata/dialnorm will be available in the VANC portion of their high-definition SDI signals.)
Knowledge is power! I made up a cable with nine-pin plugs and connected the Tiernan to the LAMBDA. It was a beautiful site. At once I was able to read NBC's dialnorm value of –23, displayed above the ITU loudness level on the right side of the display (which indicated –16 at that moment). In addition, there was a horizontal line indicating the DN level across all channels on the display, just as there was for the ITU loudness level. The two lines operate independently of each other, and each line has an indicator label associated with it.
In addition to the dialnorm data, other information was available from the RS-485 metadata as well. Looking under the MetaData menu, there was a list of several pieces of data associated with the program. Some of the information included was: Pgm Config IE:5.1, Frame Rate IE: NTSC, Bit stream Mode, Coding Mode, LFE on/off, Dialog Level, Center Down-mix info IE: –3.0, Copyright Information, Original Bit Stream Verification and Room Type, just to name a few.
When the Signal Status screen is selected, at a glance you can see information such as MetaData Present, Data Source, Program Type, while "mini meters" are visible to confirm program content while you are away from the main audio level monitoring screen.
Operation of the LAMBDA is intuitive, logical and easy to learn.
In short, the LAMBDA is a top-shelf piece of gear. It (and units like it) are definitely the future of broadcast facility audio monitoring. There is a learning curve for guys like myself, and thanks to energetic and creative industry leaders such as Linear Acoustic, there are resources and tools that make the pathway to the future a little less scary.
Joey Gill is chief engineer at television station WPSD in Paducah, Ky. He has been with the station for 25 years and has worked in broadcasting since 1977. He may be contacted at [email protected].