If you have not seen this Youtube video, put down the coffee (or whatever) and move any spill able things away from the keyboard and enjoy:
As it turns out, 300 kbp/s or greater. At least in critical listening environments according to the paper titled Perceived Audio Quality of Realistic FM and DAB+ Radio Broadcasting Systems (.pdf) published by the Journal of the Audio Engineering Society. This work was done by group in Sweden and made various observations with different program material and listening subjects. Each person was given a sample of analog FM audio to listen to, then they listened to various audio selections which were using bit reduction algorithms (AKA CODEC or Compression) and graded each one. The methodology is very thorough and there is little left for subjective interpretation.
In less critical listening environments, bit rates of 160-192 kbp/s will work.
I made a chart and added HD Radio’s proprietary CODEC HDC, which is similar to, but not compatible with AAC:
|System||Codec||Bit Rate (kbp/s)|
|HD Radio FM; HD1 channel*||HDC (similar to AAC)||96 – 144|
|HD Radio FM; HD2 channel*||HDC||24-48|
|HD Radio FM; HD3 channel*||HDC||24-48|
|HD Radio AM*||HDC||20-60|
|DAB+||AAC/HE-AAC||32 – 128|
|DAB||MPEG II, Dolby digital||192 – 256|
|DVD||PCM, DTS, Dolby digital||>800|
|Web Streaming||MPEG I,II,III, WMA, AAC, etc||32-320, 128 typical|
|iTunes||AAC||128 – 256|
|Spotify||Ogg Vorbis||96 – 320|
|Wimp||AAC/HE-AAC||64 – 256|
**PCM: uncompressed data
This is the composite Mean Basic Audio Quality and 95% confidence intervals for system across all excerpts:
Over the years, we have simply become accustomed to and now accept low quality audio from mp3 files being played over cheap computer speakers or through cheap ear buds. Does this make it right? In our drive to take something good and make it better, perhaps it should be, you know: Better.
Special thanks to Trevor from Surrey Electronics Limited.
UPDATE: I notice that Radio World has a little star rating system on their articles. According to the rating, twenty one people think I suck… That is okay, but when I started looking around at all of the other articles on the website, I noticed most have but one or two votes. It seems odd to me that my little opinion piece would have so many negative votes, especially in light of the e-mails, phone calls and personal interactions I have received supporting my position.
Perhaps a few of you could run over there, read the article then objectively decide what you think… Here is the link: AM Efforts Should Include Tech Solutions
I am deeply immersed in all things networking, yet again. I regret the sparse posts, but there are a few things of note:
- It appears the the WYFR shortwave site in Okeechobee has been sold to the operators of WRMI (Radio Miami International). This is a good turn of events for shortwave broadcasting. WRMI programmed mostly to the Caribbean and were difficult to hear in these parts.
- Nielsen Radio, formerly Arbitron, says it will increase the sample size for the PPM program. This is good, larger sample size means better accuracy and fewer extrapolation related errors and strange rating spikes.
- I published an commentary in Radio World Commentary: AM Efforts Should Include Tech Solutions. What do you think? Should the industry be looking at something other than HD Radio?
- Then, from across the pond there is this:
Which is a digital radio promotion from the BBC. It seems Great Brittan is trying to force an all digital transition. A glimpse of things to come?
- In spite of the lack of posts, the blog continues to grow, averaging 550 to 600 page views per day with about 180 RSS subscribers. As far as content goes, I can assume more of the same will suffice.
As time becomes available, I will post more.
A little blast from the past. This was found in a transmitter manual at one of the sites we take care of:
I thought I would scan it and make it available here. As luck would have it, there is also a corresponding piece of equipment to go along with it. I had never seen a “CCA Optomod” (.pdf) before I was working at one of the radio stations in Trenton, Florida. This unit was rescued from under a pile of garbage out in the lawn shed. It was full of mud was nests and mouse droppings. Needless to say, it required a bit of TLC to return it to operation. I replaced the electrolytics, cleaned it up and ran some audio through it. It is probably as good as the day it left the factory. Bob Orban made some really good stuff in his day.
The original Optomod 8000 was an evolutionary design that made FM radio processing what it is today. The idea of combining broadband limiter, AGC and stereo generator in one box was a radical departure from the norm. The audio limiter functioned as a 15 KHz low pass filter and broadband AGC.
The stereo generator used very modest amounts of composite clipping to reduce overshoot and transients. Many people disparage composite clippers. If done correctly, it is transparent to the listener and increases perceived loudness by stripping off modulation product that is non-productive.
Some thirty five or so years later, there are still many of these units in service in various stations around the world.