Can people please run the following test on their boxes and report what they are using and what they hear:


box: Echostar
cable: hdmi
avr: onkyo

I hear a hum during the quiet parts or silence of a programme, BUT IF I PAUSE THEN THE HUM DISAPPEARS.

This is most noticeable through an amp rather than the TV's own speakers. In fact you cannot really notice it via the TV's speakers or via the amp when the amp is soft.

It is apparent on both Dolby and aac/mp3 sound formats from the box.

As the hum disappears when you pause a recording or live TV suggests the speakers are correctly wired and noise is not being introduced there.

The symptoms you describe are consistent with the "hum" being part of the broadcast signal. Can't say I have noticed it here on my Humax Foxsat HDR.

I would hope it is not part ofthe broadcast signal as that would show a very poor noise floor, so I doubt that.

I do not think the hum is there from my freeview, but as that is built into my TV, I route that to the amp via phono leads (so not the digital source from the broadcast).

If you set the amp volume to a level where the hum is audible then change channels on the receiver does the level of noise change at all with the channel? If it does then it is possibly the broadcast signal introducing the hum.

Different broadcasters process the audio signal differently so there should be a noticeable difference in the noise floor depending on how hard they are compressing the dynamic range of the audio source.

If however the noise is fairly constant then I would suspect the amp. It is entirely possible that when presented with no digital input (possible when you pause the programme) it could mute the amp stages to prevent any nasty noises as the audio returns after you resume playing.

Though if it was the amp it should be present on any source. So if you have a DVD or Blu-Ray player plugged up or some other digital device then they should "hum" in the same way. It could of course be the Echostar box. But if it kept the audio entirely digital from in to out then it should not really be imposing a hum on the signal. Hum is more usual on all analogue systems or where there is an analogue stage in an otherwise all digital system.

Dolby Digital (AC-3) is encoded. Unless the device includes both a decoder and a (re-)encoder, there is no way a STB or DVD player can change the signal in any way if it's output in this format. You get exactly what's broadcast, because the device has absolutely no way to change it.

If it's decoded to PCM for output, it could in theory change it - but it won't. It certainly won't add a hum.

Some receivers/DACs used to mute internally when they receive digital silence, as a trick to maximise dynamic range measurements (it makes silence perfectly silent! ) - I don't know if any still do. It's possible/probably that your set top box is sending digital silence when paused.

Cheers,
David.

@2Bd:
agreed, it is either taking a mp3/aac signal and decoding to PCM or bitstreaming ac3
in which case I am not sure why my other digital sources (eg PC) do not produce such a high hum.

However I like your rationale for the digital silence and dynamic range as it is certainly very audible at high volumes so many dBs of range!

As a final test I'll output the Echostar via phono cables and see how it sounds and report back, but that will be next week as I'm away for the w/e

only time I had a hum, is when the STB was not earthed. Sensitive amp was picking up the hum. Once earthed properly, it disappeared

hmm, good thought.
As it happens my amp came with a 2 wire (EU) plug and a convertor (I think that is the way Onkyo sell there UK/EU stuff.

Pretty well all AV kit is double insulated so no earth connection. Indeed if you have more than one earth bond it is likely to create hum. More than 1 earth allows any induced voltages (usually at 50Hz) to produce a a current.

My new Onkyo stereo amp for the bedroom turned up today. Two pin plug with no converter. Used a travel converter I happened to have but blew the fuse in that which I forgot was only 1A.

Must be a grey import, UK sold kit has to have a BS1363 and a ASA kite mark 13A plug fitted, or a approved two pin to 1363 adaptor included.

yes mine had an adaptor included and the box part no was uk.

You think it is worth giving Superfi a ring to have a moan at them? TBH I was relieved when I realised that it was the 1A fuse that blew as I spent a few minutes cursing Onkyo and Superfi for giving me an amp that only lasted five minuets.

Certainly worth a call. I would check with Onkyo, most manafacturers won't have a bar with grey imports leaving your warranty rights purely with the supplier. Superfi should have made it clear that the kit was a grey import and therefore not fully compliant with UK specs.

Superfi are sending me the missing adaptor. So that's all good.