Query on crackpot scheme for recording audio with extended bandwidth

[KiM3Ce]

This may be a really stupid question but that's how we learn, right?

According to https://en.wikipedia.org/wiki/YPbPr, a component video input has:

Y: carries luma and synchronization
Pb: Blue minus luma
Pr: Red minus luma

I would like to use a DVR to record a composite FM signal, which has a bandwidth of of 53 KHz.

I don't care about the video, I just want to record the composite. I'm experimenting with FM decoders, which convert the FM composite signal to stereo audio.

It's easy to take the composite FM signal from any tuner that has an MPX output jack or oscillosope outputs; the composite is the horizontal scope signal.

I don't expect a DVR will record without sync. If I feed the Y input on the DVR from the Y output on a cable box, that should (I hope) enable recording.

If I feed composite FM to Pb or Pr, the DVR should record it. The bandwidth of a Pb or Pr video signal should be much larger than the 53 KHZ FM signal.

On a typical DVR, how is are the Pb and Pr stored? How many bits? What sampling frequency?

Yes I know I could just record the audio, but I want a stored FM composite signal so I can compare FM MPX decoders. It seems like hijacking a DVR is a lot easier than cobbling together a recorder that can record the FM Multiplex signal.

Here's more on that signal if you want it:

https://en.wikipedia.org/wiki/FM_broadcasting

Thanks is advance!

[old_tv_nut]

The question I can't answer is: does the DVR record the signal during the blanking intervals? If not, your continuous FM signal will have big bites taken out of it.

[KiM3Ce]

After a little research, I can see that this is not practical. I was thinking the DVR was like digital audio where you sample and store a stream of data. The data storage on a DVR is all structured around frames, not designed to produce a smooth stream of output. The conversion to frames and back will probably not provide a good replica of the input. Ironically, a VCR might do the job. Thanks old_tv_nut!

[Electronic M]

You may be able to do this with SDR (software defined radio) many SDRs can record the continuous RF signal and replay and low power retransmit the RF signal. You have to pick your ADC/DAC carefully if you want post detector recording, or buy a mixer/oscillator to heterodyne the signal between it's Actual frequency and a frequency the DAC/ADC can process.

It's also possible on some high end reel tape recorders to record up to 100khz IIRC.

[KiM3Ce]

Thanks! I'm thinking a modern data acquisition system might not be prohibitively expensive.

https://www.ni.com/en/shop/data-acquisition.html

Ideally I would like to do the digital signal processing like the Accuphase tuners do, without buying a $9,500 tuner :-).

https://www.accuphase.com/tuner.html

[Electronic M]

Originally Posted by KiM3Ce

Thanks! I'm thinking a modern data acquisition system might not be prohibitively expensive.

https://www.ni.com/en/shop/data-acquisition.html

Ideally I would like to do the digital signal processing like the Accuphase tuners do, without buying a $9,500 tuner :-).

https://www.accuphase.com/tuner.html

I don't have time to verify specs (got a swapmeet tomorrow), but you have to be careful with laboratory data loggers. Most do NOT record the actual signal but simply create an Excel or .CSV file containing the input voltage every so many seconds or mS...My last job was as a test engineer and I regularly used Agilent and DataQ data loggers that worked as described above and were not capable of recording a continuous audio waveform.

If you aren't married to using any specific tuner to capture your FM station SDRs can receive the raw RF from the air and digitally demodulate the FM stereo signal to audio on your PC....They can also decode the RDS data and HD radio signals hidden in the FM carrier.
Odds are that obscenely expensive tuner is basically a small embedded Linux computer running an SDR, high quality DAC and a fancy user interface.

[KiM3Ce]

Thanks!

[KiM3Ce]

You might get a chuckle out of this:

Instrumentation science & technology, Vol.43(2), pp.214-221
03/04/2015

We have developed a complete 100kHz ultrasonic recording system. The primary components of the system are a SensComp Series 600 Instrument Grade Electrostatic Transducer, custom printed circuit board (PCB), wide-bandwidth instrumentation amplifier, linear-phase filter, fully differential 16-bit analog to digital converter (ADC) sampling at 840kHz, 168MHz STM32F4 32-bit microcontroller, and a direct 100Mbps Ethernet connection. A host computer running a custom application written in C++ provides a unified computer interface that allows the user to control all aspects of the system and provides a real time spectrogram. The system is designed for general use but has been initially used to study the ultrasonic vocalizations of rodents. We demonstrate the system by recording a well-established call made by Long-Evans rats termed 50-kHz vocalizations.

I wonder if they're finished with it. Maybe I can buy it used :-).

[ARC Tech-109]

I guess the one question that stands out is why the need for a high resolution recording for a broadcast audio signal? What you hear on the air is less quality than a 192K mp3

[Phil]

"What you hear on the air is less quality than a 192K mp3 "

I would have to disagree with that statement. On what do you base this?

[ARC Tech-109]

Because most of what is broadcast IS sourced from mp3 playback.

[Electronic M]

Originally Posted by Phil

"What you hear on the air is less quality than a 192K mp3 "

I would have to disagree with that statement. On what do you base this?

It's been around 15 years since I read this but my first MP3 recorder (at the time I didn't have a PC so recording analog audio was the only way I'd have MP3s) was a Pogo Products radio your way LX and it was basically the radio equivalent of a DVR. IIRC the manual and C Crane who I bought it from (they later made a CC radio version of it that I wish I had bought) recommended 64Kbps or 128Kbps for FM radio but didn't give much justification...

[ARC Tech-109]

Long live the Optimod

[Phil]

Actually, I am the engineer for several stations AM, FM and SW. Every AM and FM I have anything to do with or of which I am personally aware uses uncompressed PCM 44.1 khz, 16 bit. Stations in the three markets I deal with quit using MP3 for on air use years ago when disc storage became inexpensive (relatively).

[ARC Tech-109]

Most of what we deal with in the common markets is still mp3 based, even with a real 44.1/16 source there's some degradation in the chain from source to xmitr and while the broadcast gear is many steps above the consumer electronics the losses are still a factor in the big picture.
I miss the days of packing fidelipaks...