Tag: HD radio

HD radio aka IBOC, ibiquity’s digital radio scheme

Brother, can you spare a theorem?

A theorem is not, indeed, a fact.  It is rather, an idea that is deduced and supported by other proven facts.  Thus, a theorem is generally believed a truth.  It should be of interest to the “All Digital” AM (AKA Medium Wave) proponents that noise on the digital channel will reduce data throughput as a function of channel bandwidth and Signal to Noise Ratio.  This is known as the Shannon-Hartley theorem:

C = B \log_2 \left( 1+\frac{S}{N} \right)

Where:
C is the channel capacity in bits per second;
B is the bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated carrier), measured in watts (or volts squared);
N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and
S/N is the signal-to-noise ratio (SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian noise interference expressed as a linear power ratio (not as logarithmic decibels).

With this equation, one can discern a fundamental flaw in all digital logic.  One of the main issues with AM Medium Wave broadcasting is the ever-increasing noise floor.  Our society has changed drastically in the last one hundred years or so since AM was invented.  Electrical noise generators; computers, plasma screen monitors, mobile phones, appliances, energy-efficient lighting, data over power line, street lights, poor utility line maintenance, and even electric cars, it seems, generate a cacophony of noise in the Medium Wave frequency band. A digital modulation scheme, be it HD Radio or DRM, will mask the noise to a certain extent, that is true.  However, once the SNR exceeds the ability of the receiver to decode the necessary bits, the receiver will mute.  While it is true, the listener will not hear noise, they may not hear anything at all.

I will also note; none of the current “AM improvement” schemes under consideration by the FCC addresses the noise issue on the AM band.  Without addressing the noise issue, any digital modulation scheme will be a temporary fix at its very best.  The noise floor will continue to rise and after it gets high enough, the all-digital modulation will simply not work.

It will be interesting to see the data from the all-digital HD Radio testing that is being done in various locations.  That is, if the NAB, et al. does not decide to treat that data like some kind of state secret; they have become reticent of late.  When somebody acts like they have something to hide, it makes me think they have something to hide…

CES 2014 and the Digital Radio question

I have been busy of late, however, still keeping abreast of the news of the day.  Along with that, CES 2014 wrapped up recently.  No huge developments, especially when it comes to Broadcasting.  However, there was one item of interest; the updated technical specifications of IEEE 802.11ac.

It is of interest here because of the implications of mobile/portable data developments and their impact on traditional AM and FM broadcasting. The new specification calls for 1.2 Gbp/s per device in the initial release, increasing that throughput to 6 Gbp/s in later releases.  These data rates are for overall transmission, including the WiFi overhead.  Actual usable application data (layers 5-7) would be about 20 to 30 percent less.  Even so, 900 Mbp/s is a phenomenal data rate.  Truly I say to you; this is the future of digital broadcasting.  HD Radio™; may well prove that the “HD” stood for “Huge Distraction.”

The new 802.11ac specification uses MU-MIMO, high-density modulation, larger channel bandwidths, and beamforming technology in the 5 GHz WiFi spectrum.  Of course, the question is, at what distances will this system work?  If it is like conventional WiFi, then 100-200 feet is about all that can be expected.  However, there are also many people interested in wireless broadband (WiMAX) service as an alternative to traditional wired ISPs. For that application, having many outdoor 802.11ac nodes connected by a backbone could potentially blanket a city or campus with free high-speed wireless data.

Example of cjdns network
Example of cjdns network

Along the same lines, there are many people involved in creating mesh networks of various types; be they ad-hoc mobile networks, darknets, bitclouds, etc. Mesh networking is a very interesting topic, for me at least.  The network protocols are getting better and more secure.  WiFi hardware is becoming less expensive and more reliable.  As more and more people put effort into developing protocols like cjdns, local mesh networks will become widespread unless they are outlawed.  You know; because of teh terrorism!!1!!

As it stands today, I can drive for two hours in mostly rural upstate NY and CT streaming my favorite radio programs and have nearly seamless handoffs and very few dropouts.  This is on my three-year-old, beat-up 3G HTC android phone sitting in the passenger seat of my car.

Digital Radio is here, it is simply not the In Band On Channel system that legacy broadcasters have chosen.

What bitrate is needed to sound like analog FM?

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 a group in Sweden that 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:

SystemCodecBit Rate (kbp/s)
HD Radio FM; HD1 channel*HDC (similar to AAC)96 – 144
HD Radio FM; HD2 channel*HDC24-48
HD Radio FM; HD3 channel*HDC24-48
HD Radio AM*HDC20-60
DRM30 (MF-HF)AAC/HE-AAC34-72
DRM+ (VHF)AAC/HE-AAC700
DAB+AAC/HE-AAC32 – 128
DABMPEG II, Dolby Digital192 – 256
Blu-rayPCM**≥6 Mbp/s
DVDPCM, DTS, Dolby Digital>800
CD-APCM1,411
Web StreamingMPEG I,II,III, WMA, AAC, etc32-320, 128 typical
iTunesAAC128 – 256
SpotifyOgg Vorbis96 – 320
WimpAAC/HE-AAC64 – 256

*Hybrid mode
**PCM: uncompressed data

This is the composite Mean Basic Audio Quality and 95% confidence intervals for the system across all excerpts:

digital-analog-audio-compar

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.

A few updates

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:

  1. It appears 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 was programmed mostly to the Caribbean and was difficult to hear in these parts.
  2. 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.
  3. I published a 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?
  4. Then, from across the pond there is this: