I’m running Audacity 2.0.5 on Windows 7 (little 2GHz atom-powered PC).
Outboard USB sound card (cheap): http://www.sweex.com/en/assortiment/sound-vision/sound-cards/SC016/print/
The sound card is a bog-standard type with 16-bit recording - about 90dB SNR - good enough for recording my old cassette tapes.
I have a mix of cassette tapes. Some early recording I’ve made I didn’t bother setting the recording level on - just blindly recorded from line out on the deck to line in on the sound card.
There are SIGNIFICANT clipping marks all over the recordings of these loud tapes.
Any yet… when I play back I don’t get any appreciable distortion - the recording sounds as good as the tape did.
I’m not using a cheap and nasty cassette deck either - an Aiwa AD-R460 which has had a head change and recalibration - they used to sell for GBP £150 back in the 1980s.
I know hi-fi and what it should sound like - and I assumed a clipped digital recording would sound terrible - very “crunchy”.
But these recording sound absolutely fine.
Does Audacity have some secret (hidden) headroom built in? Is the 0dB level actually -3dB or something with respect to full-scale saturation of 65535 (+/- 32768) on a 16-bit ADC as would probably be in by sound card?
You mean red vertical lines when you turn View > Show Clipping on? That shows a line for every single clipped sample. If there are no more than three successive clipped samples that clipping won’t appear on the Meter Toolbar clipping indicator and probably won’t be audible.
Or do you mean the waves are flat-topped?
No and No.
I think the waveforms are flat-topped. To be honest, I haven’t zoomed in enough to see the actual traces. Zooming out to view the entire 45 minute recording shows a mass of dark blue virtually filling the +1 / -1 recording scale and when I turn on “view clipping” there’s a sea of red - almost 50% of the traces at a 45-minute view turn red.
Any yet - I listen to the audio on playback through some nice headphones or back through my hi-fi (very expensive £1000 amp and £500 speakers, all-be-it old ones) the recording sounds as good as the tape.
I would expect with that much clipping for the audio to sound like an amplifier that’s gone into clipping - very harsh, “crunchy” drum beats and unlistenable.
And yet - the track sounds identical to the tape. Yes the bass is heavy and the music sounds compressed somewhat with a lack of dynamic range - but no worse than the tape did.
Perhaps I got used to a bad, loud recording. Perhaps the tape deck itself is clipping because the analogue circuitry is running out of headroom. If Audacity is doing no more than the same, I suppose it’s not going to make anything sound “worse”.
What’s the full story?
You recorded the tapes, trimmed and Normalized the recording, then exported as MP3, and now when you open the MP3 files you see red clipping lines over 50% of the track?