TV and Hi-Fi

I think it is because the implementation of FM reception on some modern tuners is entirely digital as software defined DSP radio implementation rather than a classical analogue circuit (where delay is negligible).

Tuners sold as DAB tend to have this problem more than most. It manifests as curious flanging effects as you move between the sound fields of different radio receivers. It wouldn't surprise me if mobile phones used a software solution for FM reception.

Different DAB tuners show it much more profoundly.

The ADC can do a conversion in one sample time. If sampling at 48KHz, the delay to make digital is the time period of one clock cycle.

That's not where significant computer audio delay comes from. At that level, we're talking a few clock cycles here and there (say 20us to 60us or so). You need time for the sharp cutoff analog filter, a time for the sample and hold, then the conversion cycle.

Computer audio delay, comes from interrupt handlers and in effect, "packet buffers". The driver sends a few hundred bytes to the sound card. When the buffer is half empty, the scheme requests another packet. The idea is to have a fifo buffer, where there aren't any overruns or underruns. The size of the buffer determines how many interrupts per second will result. And across all OSes, the buffer has been set to a rather large value at times. I don't have a collection of numbers for this (in Linux you could adjust this in ALSA).

Packet buffers reduces the overhead. If you had to raise an interrupt for every byte of data, there would be

All computer audio has latency (a latency you can hear or experience). Not all hardware devices by themselves though, have latency. If you had an ADC tacked in line with a DAC, the latency through there would be quite small and would not appear to affect lip sync on a TV set.

The video latency through your LCD monitor, is around four frame times or so.

The next time a computer mis-behaves on you, well, there's a lot of crazy stuff going on, and not very good odds of the computer doing a nice job. Sorta like those LED lightbulbs we bought, that take three seconds to turn on. Great idea, but "heavily taxed". A latency tax.

The computer isn't always available when you want it to be. People building "audio workstations", verify their build with DPCLAT. The computer this was collected on, when the desktop is idle, only the shortest of the green bars is present in DPCLAT. This means the computer could be used as an Audio Workstation. However, you can't record audio and play a 3D video game, without the possibility of a click or pop in your recording effort. Measuring the Delay Procedure Call latency, indicates whether the computer is responsive enough for real time work.

And just for the record, the video card should not be allowed to do that. Those tall red bars. Somebody should give NVidia a smack.

Paul

There doesn't need to be digital processing. Back in the day delays were extremely short - a few microseconds at most - on analogue type filters and decoders. But it may be that if you can turn an FM signal into a sampled digital signal somewhere in the high kilohertz band then you can apply digital filtering and decoding to that . I know that you can use a digital TV dingle to recieve FM...

Well, it would be.

colour TVS were degaussed ...on switch on. Probably after a few hundred more that would have faded.

Well, digital radio mics are well known for a degree of latency. Not really a problem if used on their own, but can cause unwanted effects when mixed in with pure analogue ones. The ear can hear a tiny delay when both can be heard together.

Good reason not to buy new then. ;-) Since non of mine exhibit this.

As do Freeview TVs both tuned to the same channel.

Both receiving FM radio through their radio tuner circuitry. denon connected to home-brew FM aerial in loft, Phillips using its antenna aerial.