Jeff Keith

You know what a sine wave looks like – and it sure as heck isn’t square. Which, frankly, is more than we can say for a lot of the source CDs that you have to somehow pass as quality on-air programming these days.

No doubt about it. The quality of CDs and other source material has been on the decline in recent years. Recording studios used to master at a 20 dB peak-to-average ratio. These days, it’s closer to 6 dB. So, what can you do? Plenty, according to Wheatstone’s Broadcast Audio Perfectionist, Jeff Keith.

• Keep a level head. About 18 to 20 dB headroom throughout the air chain should do, whether the studio is analog, digital or a mixture of both. This will give you enough peak headroom above average operating levels to keep distortion in check when those source levels run hot. And they will.
• Set the audio gains within your air chain so that each piece of equipment reaches its clipping point at the same time. This gives you optimum dynamic range and you might even gain a little sound depth and detail along the way.
• Balance left/right channel levels, differences of which can generate artifacts in the stereo sound field.  Channel imbalances are especially problematic for mono material because even slight level differences in live or recorded voice, for example, can create additional L-R information that ends up as distortion in the stereo field.
• Use bit-rate reduction and codecs sparingly. This is doubly important now that source material is more densely compressed, which makes it more difficult for codecs to determine and therefore remove only the insignificant audio that our ears might not notice. One codec in the air chain is probably necessary. But running the result through another codec is just asking for it.
• Go for linear instead of bit-reduced music storage. A lossy codec at a 4:1 compression ratio takes away almost three-quarters of the audio waveform. Don’t go there.  The cost of hard drive storage went from around $100/gigabyte to $0.01/gigabyte in recent years, so use those gigs for linear audio storage.
• Resist the temptation to air or stream low bit-rate MP3 files from the internet, no matter how new and hot the song. Enough said.
• Use multiband EQ to cover a multitude of mastering sins. Applying selective EQ to hotly compressed cuts can improve the sense of dynamic range and make it easier for any codec in your air chain to determine which bits are critical to the ear and which can be removed without your ear noticing. Remember that the songs cut today and those that were cut in the ‘80s are decibels apart in just about every way, so a little equalizing in just the right places can get them to meet somewhere in the middle for a more consistent on-air sound.
• Back off on limiting and clipping. You don’t need as much as you did in the old days.  Your friends in the recording studio have done plenty of that already.
• Eliminate troubles. If it’s bass you’re missing, there’s a good chance you’re trying to make up for it with EQ in the on-air processor. If your bass settings seem like a lot, they most likely are and there is trouble elsewhere. Find the culprit through a process of elimination. Jeff recalls one broadcaster who called to say he had the low-end EQ cranked up as much as he could get it, but his station still sounded thin on the air. “I suggested he listen to just the output of the console and sure enough, the bass was there. It turned out that he had a processor purchased in the ‘80s sitting upstream in the rack getting nice and toasty. Over time, the coupling capacitors kept getting smaller in value.  Unfortunately, when the capacitance goes down, the reactance goes up and the bass goes away. Problem solved,” says Jeff.
• Check frequency response. If something doesn’t sound right, start at the source and analyze the frequency response of the entire air chain. Stations with all analog gear should be able to achieve a frequency response flatness of better than +/- 1 dB between 30 Hz and 15 kHz. Stations with all digital air chains will typically measure an order of magnitude flatter (+/- 0.1 dB) response and those with a mix of analog and digital gear will typically see numbers somewhere in between. These days, you don’t need expensive test gear to do this. Check out Jeff’s article on everyday studio and software tools you can use to proof the air chain.
• Do an audio proof.  Seriously. (See above.) If you have to change equipment settings often, you need to do an audio proof. If you have distribution amplifiers that haven’t been benched in years, bench them and proof them. The same goes for mic processors, audio consoles, and any and everything that passes audio. Most of the analog equipment is suspect, but keep in mind that DSP gear has to bring in the signal somehow, and analog components age in DSP equipment same as they do in analog gear.
• Go IP all the way. Ditch the sound cards, and use software drivers for automation-to-AoIP communication when possible. Our AoIP BLADEs use 24-bit audio and taking advantage of this capability can help retain a competitive and dynamic sound.